In Croc's initial string of appearances, a Batman and Detective Comics crossover story arc that culminated in Jason Todd adopting the mantle of Robin, he was depicted as an unnamed, shadowy figure in a trenchcoat. A ruthless criminal who wants to become the crime kingpin of Gotham City, Croc works behind the scenes using methods like sniping to eliminate his criminal competitors. He briefly is in competition with a small army of Batman villains under the leadership of the Joker. When Batman finally confronts his mysterious foe, the villain is revealed to have a massive physique and reptilian appearance. It is then revealed that his real name is Waylon Jones, born with a form of atavism that imparted him with reptilian traits. His drunk aunt grew to hate her nephew's hideous appearance and brutal behavior. While still an adolescent, his aunt abused him and bullied him by calling him names like "lizardboy" and "a reptilian freak". Croc killed his aunt and became a criminal. After countless killings and biting off Aaron Cash's hand, he faced off against Batman and the new Robin, who defeated him.
In these original, pre-crisis appearances, Killer Croc resembled a powerfully-built man covered entirely in green scales, but was still basically human in his facial proportions and build. He was also originally depicted as gunning down Jason Todd's parents (this was later retconned to make Two-Face their murderer). His appearance and personality have become increasingly bestial, explained in the comics that his disease has slowly robbed him of all identifiable human traits. In his most recent appearances, he has an elongated snout and tail.
In Batman #489, Killer Croc attacks a shopping mall. After delivering several blows to Croc, Batman is distracted by a glimpse of Bane. Croc then grabs Batman and tries to break his back again. He fails, and Bane pits himself against Croc, breaking his arms. He is then put back into Arkham Asylum.
When Bane breaks the inmates out of Arkham Asylum in the Knightfall saga, Croc attempts to get revenge on Bane. While in the sewers, he smells Bane and goes after him and the two fight each other atop a ledge. Bane casually breaks one of Croc's arms again, but Croc keeps fighting him through it until the ledge they are standing on breaks and the two fall into the sewers. The fight ends up as a draw. Croc later returns, attacking the docks to try and lure Robin out, but is defeated by Dick Grayson (now acting as Batman after Bruce defeated Valley before taking time off for self-analysis) without realizing that he is facing a new Batman.
In a storyline that ran in Batman #521 and #522, Croc is summoned by a paranormal force to break out of Arkham and make his way to the Louisiana swamps. Batman follows him there, only to find that the mysterious force is actually Swamp Thing, who offers Croc a place in the swampland where he can finally give in to his animal side and live free from human persecution.
Killer Croc has appeared in both the Hush storyline and its chronological follow up, Broken City. In the former, he is infected with a virus that greatly increases the rate of his devolution, 'overseeing' a kidnapping for Hush before Batman defeats him.
In 2005's Detective Comics #810, Killer Croc attempts to cure his condition. When the doctor fails, Croc devours her.
One Year Later during the Face the Face storyline, Killer Croc is shown to have been feeding on the dead body of Orca. He next shows up in Countdown where he breaks free from his shackles in Arkham Asylum and attempts to kill Jimmy Olsen, who uses elastic powers to escape. Killer Croc is then subdued.
He is later seen among the exiled supervillains in Salvation Run. After the Martian Manhunter is defeated and imprisoned in a fiery cage, Croc suggests that he eats him. Lex Luthor forbids it however.
During the Final Crisis storyline, Killer Croc can be seen as the member of Libra's Secret Society of Super Villains. Killer Croc is later turned into a Justifier.
In the Battle for the Cowl storyline, Killer Croc is recruited by a new Black Mask to be a part of a group of villains aiming to take over Gotham.
During the events of Brightest Day, Killer Croc is accidentally released from his cell by a guard whom Osiris kills when Deathstroke and his band of Titans infiltrate Arkham. While attempting to flee from the facility, he is attacked by Osiris who mistakes Killer Croc for his old enemy Sobek.
The New 52
In this timeline of The New 52, Killer Croc makes an appearance in the flash back in Roy Harper's memories, having the head of a crocodile. He is seen fighting Roy in Hell's Kitchen but quickly notices Roy isn't fighting back. He figures out that Roy's trying to have him commit assisted suicide ("death by croc"), and comforts the ex-sidekick knowing Oliver Queen screwed him over publicly by taking his shares of Ollie's Company and tells him that this is not the way to go out. Roy says he was not that bad of a guy before blacking out, but Killer Croc reminds him next time he will not be so nice. He is then passingly referenced by Roy as he is Roy's current sponsor for his alcoholism at the time when Roy was in a bar with Jason Todd. Roy is only drinking water, but knows Waylon would disapprove.
Powers and abilities
Killer Croc's backstory explains that he was born with a condition resembling epidermolytic hyperkeratosis, a disfiguring skin disorder. However, it is actually a form of regressive atavism, meaning that he has inherited traits of ancestral species of the human race such as reptiles. This condition has been augmented by the presence of a metagene. Consequently, he has several extraordinary physical abilities relating to his endurance, strength, and speed.
His skin is hardened to the degree that it is nearly impenetrable to ordinary forms of abrasion including high caliber weapons fired from a distance. He possesses a degree of super strength; for example, he was able to tear a bank vault door off of its hinges with minimal effort. He has demonstrated regenerative powers allowing him to heal and restore lost limbs and teeth. He possesses superhuman reflexes and speed, especially while he is moving underwater. Killer Croc also has an enhanced sense of smell. Once he has become familiar with a person's scent he can track them from miles away. As his appearance and personality has grown more and more bestial, his misanthropy has increased dramatically. He is jealous and hateful of "normal" people and often lashes out violently without provocation.
Croc's main weakness is consistently portrayed in most adaptations, aside from The Batman series, as being his low intellect. He typically resorts to brute force to solve most of his problems, allowing Batman to outmaneuver him in combat by thinking his way through the problems he faces in defeating the powerful Croc. Batman regularly describes his foe as an animal rather than a man. He acts almost solely on instinct and hardly ever takes the time to plan or rationalize his actions.
In recent years, Killer Croc has been portrayed as being much more reptilian than in past incarnations. An action figure made by Kenner in 1998 featured a tail and dinosaur-like feet. When Mattel got the license to make DC products in the early 2000s, they released their own version of Killer Croc, sculpted by Four Horsemen Studios. This version also featured a tail and dinosaur feet. In late 2005, a re-release of this figure was modified so that the tail, along with his shirt, was removed. This version also sports a more "human" head.
The 2002-2003 Batman storyline Hush featured a more bestial Croc who had been mutated against his will to appear more reptilian. This version of the character was drawn by artist Jim Lee.
In The New 52 he is shown to have a crocodile-like head, though how this came to be has not yet been revealed. Such a design had previously appeared in Red Hood and the Outlaws drawn by Kenneth Rocafort.
Joker graphic novel
In the non-canon graphic novel, Joker, written by Brian Azzarello and artist Lee Bermejo, Croc is portrayed as a thug, a large, muscular African American man with a scaly skin condition. Of all his previous designs, this is the most human. He is missing his abnormally long snout, tail, and claws. However, the book seems to hint that this Croc enjoys feeding on human flesh, with the story's narrator remarking that Croc "has a certain... eccentric way with evidence". Croc is shown leading a gang of thugs, and later becomes a high-level member of Joker's newly formed gang. This vision of the character is not unlike the one from Azzarello's previous work on Batman, Broken City. 
In the Batman Beyond comic, Killer Croc is mentioned as being a prisoner in a Cadmus Labs facility; his cell is briefly attacked by the new Hush, a clone of Dick Grayson, when Hush escapes the facility before he decides to simply leave. Another Cadmus official later contemplates releasing Croc to lure Hush out, but Amanda Waller dismisses the idea due to the potential for collateral damage. 
Batman: Crimson Mist
In Batman: Crimson Mist, Killer Croc begins as a rumoured serial killer stalking Gotham's sewers, later joining Two-Face's gang as the muscle. Faced with the threat of the vampire Batman stalking and killing his opponents, Killer Croc and Two-Face form an alliance with Commissioner Gordon and Alfred Pennyworth to trap Batman in the Batcave and expose him to the sunlight (although Croc briefly contemplated just physically tearing Batman apart himself before the others pointed out that he was too fast for Croc, the vampire Batman proving more than a match for him physically when they did engage in close-quarter combat despite his withered physical condition). Although Croc and Two-Face attempt to kill Gordon and Alfred when Batman is believed dead, Alfred is able to help his old master recover by sacrificing his life and blood to give Batman the strength to stop Gotham's last criminals. With Alfred's sacrifice, Batman impales Croc with a stalactite, commenting that Croc can keep his cold blood thanks to Alfred's sacrifice having sated his appetite for the moment. 
In the alternate timeline of the Flashpoint event, Killer Croc kidnapped the people of Gotham and imprisoned them in the sewer. Batman then arrived and attacked Killer Croc. Killer Croc was about to strike back at Batman, but Batman stabbed him in the head with his own machete. Batman rescued the people that Killer Croc had imprisoned.
Killer Croc appears in several episodes of Batman: The Animated Series voiced by Aron Kincaid. Waylon Jones is a former pro wrestler who turned to crime. In this series, he is given lumpy gray skin as opposed to his normal green, teeth filed to points and his reptilian appearance is toned down somewhat. Moreover, the character is far less formidable as his chief assets (his strength and toughness) provide him with no real edge over Batman as he consistently trounces him with relative ease. In the episode "Vendetta", he runs afoul of Harvey Bullock who arrests him. He later escapes from prison and seeks revenge by framing him for the abduction of criminals Spider Conway (who Killer Croc abducted from a prison transport) and Joey "The Snail" (who Killer Croc abducted from the police station). After Batman rescued the two criminals and returned them to the police, Killer Croc went after Harvey Bullock until Batman arrived. During a fight in the sewers, Batman managed to defeat Killer Croc. In the episode "Sideshow", Killer Croc escapes from a train bound for Levitz Prison and flees through the countryside, taking refuge in a town of naively trusting circus carnies including a "seal boy" named Billy, a giant named Goliath, conjoined twins named May and June, and a hunchbackedringmaster named Richard. Although he begins to have second thoughts about it after they treat him like a family member, Killer Croc plans to betray and kill his hosts for the money they have stored away for supplies. He mentions sardonically, "You said you could be yourself out here, remember? Well, I guess that's what I was doing. Being myself." In this episode it is established that Croc is legally sane, and therefore is to be sent to Blackgate Penitentiary instead of Arkham Asylum. He also appears in the episode "Bane" in which he encounters Bane in a sewer who proceeds to beat Killer Croc up. When questioned by Batman, Killer Croc replies, "He was big". In the episode "Almost Got 'Im", a group of villains are discussing how they almost defeated Batman. While everyone else describes almost killing Batman with some kind of complex deathtrap, Killer Croc proudly proclaims that he once threw a rock at Batman. After a prolonged awkward stare from the other villains and an attempt to change the subject by Poison Ivy, he defensively added, "It was a big rock." It was later revealed though that this Killer Croc was Batman in disguise. In the episode "Trial", when Batman is put on trial by all the prisoners he's put in Arkham, Killer Croc is among the kangaroo court shouting "Hit 'im with a rock!". The episode "Sideshow" reveals a sequence where Killer Croc nearly does hit Batman with a huge rock but was drugged and couldn't throw it far enough to smash him. The rock is later referenced again in a season 3 webisode of Gotham Girls as an item in the evidence vault. Unlike most villains, Killer Croc's actual identity is never revealed, the only indication of his real identity being that his wrestling name was "Killer Croc" Morgan.
Killer Croc appeared in The New Batman Adventures voiced by Brooks Gardner. Killer Croc has been revamped with a bulkier build and green scales and skin. In the episode "Love is a Croc", he breaks out of the courthouse and goes on the attack until he is subdued by Batman. He then joins forces with criminal Baby Doll after she rescues him from a prison transport. They go to live in the sewers, committing crimes planned by Doll and carried out largely by Croc. Baby Doll falls in love with him until she overhears Croc boasting about manipulating her. Enraged, she betrays him to Batman and Batgirl and in the ensuing fight he is defeated after being drenched in boiling water. He makes his final appearance in the episode "Judgment Day" where he is seen trying to get Penguin to fence stolen jewels. A villain known as the Judge attacks and defeats him by throwing him off the top of the bridge. Batman manages to rescue Killer Croc.
In the Batman Beyond episode "Terry's Friend Dates a Robot", an android replica of Killer Croc battles the new Batman in a simulation.
Killer Croc appears in The Batman voiced by Ron Perlman. In this version, Croc is even more reptilian and crocodile-like than past versions and has a tail, although he also demonstrates a greater intellect and is much more sane and non-cannibalistic than traditional interpretations of the character due to his plan to steal money by flooding downtown Gotham by reversing pumps designed to drain Gotham canals in times of flooding. He appears to be much stronger than Batman, and much like a crocodile, he's able to stay underwater for long periods of time. His origins are mostly unknown, with Croc providing little evidence about his past beyond his Cajun accent, although one of his henchmen tells Batman that there are different rumors: That he is a genetic experiment gone awry who then turned mercenary, that he deals with the wrong kind of voodoo magic in the swamps, or that he is simply a circus freak (it is never explained which, if any, story is true). He recruits three criminals (two of whom are referred to in the credits as Vic and Freddy) as henchmen to help him flood Gotham City. Along with a Cajun accent, he has two pet crocodiles to do his bidding. Batman later deprived him of his air supply enough to be taken down and left for the police to arrest him and his henchman (remarking that "Crocs may like water but they're no fish"). In "Team Penguin," Killer Croc returns as part of the Penguin's Team Penguin (which also consisted of Firefly, Killer Moth, and Ragdoll). Killer Croc is defeated when Batman freezes the water he was in. In "Rumors," Killer Croc and his henchmen later appear as one of the captive victims of Rumor after he ambushed him and his henchmen in their hideout. In "The End of the Batman," Killer Croc, Penguin, Ventriloquist, and the Joker team up to commit a crime spree now that they are under the protection of the vigilante Wrath.
Killer Croc appears as one of the villains in the Batman: Gotham Knight segment "In Darkness Dwells". This version never speaks and is only shown while under the influence of the toxin. During the segment, it is mentioned by James Gordon that this version is afraid of bats. In this version, Waylon Jones is a cannibalisticserial killer. The urban legend in the segment goes that he was an infant born with the disfiguring skin disorder epidermolytic hyperkeratosis and that his mother abandoned him in the sewers of Gotham City. As an adult, he files his front teeth into points to compliment the reptilian appearance of his skin and becomes a circus sideshow performer. Later, now called Killer Croc, he goes on a killing spree that eventually lands him in Arkham Asylum. There, his homicidal impulses intensify during treatment by Dr. Jonathan Crane as he experimented on Killer Croc in his fear aversion therapy program. Croc escapes from Arkham and flees to the sewers along with Crane (now known as The Scarecrow) and a handful of escaped Arkham inmates. There, Scarecrow performed another experiment on Croc by injecting his fear toxin into parts of his body. When Scarecrow orchestrates the kidnapping of Cardinal O'Fallon, Croc infiltrates the church and carries him down into the sewers. Batman comes to investigate, and Croc attacks him, biting him and infecting him with the fear toxin that is coursing through Croc's own body. After a lengthy battle, Batman fends off Croc by shoving a smoke grenade into his mouth. Croc is not seen since.
It was rumored that Tom Hardy would play Killer Croc in the third sequel to Christopher Nolan's trilogy of Batman. but was dropped in favor of Bane being Croc is too unrealistic for Nolan's films.  A very subtle reference to Killer Croc is made in The Dark Knight Rises when the police officers mock Gordon and ask him if he saw any 'giant crocodiles' while he was down in the sewers.
Killer Croc makes an appearance in the negatively received video game Batman: Dark Tomorrow. He is apparently being manipulated by the Joker, attacking Batman when the Caped Crusader attempts to rescue police Commissioner Gordon from the Joker.
Killer Croc appears in Lego Batman: The Videogame as a playable character with vocal effects provided by Steven Blum. This incarnation of the character is in the employ of Penguin and possesses super strength, an immunity to toxins and is able to dive underwater.
Killer Croc is featured in Batman: Arkham Asylum voiced by Steven Blum. In this continuity, Croc is portrayed as physically larger than most of his comic book counterparts, standing at a colossal eleven feet and weighing five hundred and eighty pounds. He is interred at Arkham Asylum as a cannibalistic murderer, although his many other crimes include racketeering and the smuggling of illegal drugs. The asylum staff, who hate and fear the aptly dubbed "monster", only feed Killer Croc with animal carcasses once a week and confine him to an unused sewer underneath their facility, with an electrifying shock collar to discourage troublemaking. This solitary confinement has only succeeded in magnifying Croc's intense hatred of humanity; a psychiatrist even notes she believes he now views all people as nothing more than potential food. In addition to hating Batman, Croc also hates the guard Aaron Cash as he tried to eat the guard during a break out attempt, but only got as far as Cash's left hand before being rendered unconscious. This resulting in a constant craving to eat the rest of Cash. He appears early on in the game when he is taken to the sewers and passes Batman as he and a number of guards are escorting a recently captured Joker. He vows to kill and devour Batman before he receives a shock and is taken away. Late in the game's storyline, Batman is forced to infiltrate Arkham's old sewer network in search of rare Venom roots to devise an antidote for the Titan drug that Joker has created. Killer Croc ambushes the player repeatedly, only to be easily stunned into retreat each time by hitting his shock collar with batarangs before he can come within range to attack Batman physically. He is defeated for the final time while charging over an unstable floor, which Batman destroys with explosives, sending Croc plunging to an uncertain fate. He is also one of the villains listed on the party list.
Killer Croc appears in DC Universe Online on several occasions, one of the first being as an illusion conjured by the Scarecrow. The actual character also appears at the Cape Carmine Lighthouse, where at one point heroic players may best him and Deathstroke before being permitted to proceed. Croc may also forge alliances with villainous players, revealing that he has been hired by Carmine Falcone to assassinate Bane.
Killer Croc makes a cameo appearance in Batman: Arkham City voiced again by Steven Blum. After surviving the incidents of Batman: Arkham Asylum, he is now imprisoned in the new walled-off incarceration districts known as Arkham City. Croc has taken refuge in Gotham's maze-like sewer network, killing other inmates who wander into his domain. He is presented as notably slimmer here than his previous incarnation, likely due to an inconsistent food supply. The player can encounter Croc in a time-sensitive Easter egg - after Batman has encountered Ra's al Ghul in 'Wonder City' for the first time but before Batman leaves the sewers - in which he smells "death" on Batman and saves himself the bother of killing him, promising to come after his corpse later. Croc can also be spotted in the Iceberg Lounge combat challenge map, though the use of a remote-controlled Batarang. He sits at a table with Penguin, smoking a cigar and having a drink, but he does not speak or join in the fighting.
Killer Croc makes a cameo appearance in Injustice: Gods Among Us. In the Arkham Asylum level, if one of the characters is thrown through the cell door on the right side of the second tier, they will be attacked by Croc, Penguin, Two-Face, and Riddler before being punched by Croc into the next tier of the Arkham arena. He is also in Batman's S.T.A.R. Labs, where Batman must fight prisoners escaping from Stryker's Island before the player fights the villain. It should be noted that their appearances are based on their Batman: Arkham City looks, hinting that the game takes place in the same universe.
Killer Croc appears in Batman: Arkham Origins voiced by Khary Payton. He appears as one of the assassins hired by The Joker (posing as Black Mask). He first appears at Blackgate Penitentiary, helping the crime lord break out his imprisoned men and murder Commissioner Gillian B. Loeb. While escaping, he is confronted by Batman and the two fight on the rooftops of the prison. Batman defeats Killer Croc and interrogates him, learning about the other assassins sent to kill him. He later runs into Batman during the second attack on the prison, only to flee at the arrival of the GCPD and be taken back into custody. This younger Croc is significantly smaller than his portrayal in the other games, and more or less resembles a human (an uncertain Batman even refers to him as a "human-shaped crocodile"), implying that his mutation has not yet spread to the point where he is more monster than man.
In the novel Batman: Knightfall and Beyond, based largely on the comics storyline, Killer Croc is said to have suffered from "a raging skin cancer" that turned the outer layers of his flesh into a hardened covering when he was younger. He escapes from Arkham Asylum when Bane and his men destroy it, freeing most of Batman's major foes in the process as part of a plan by Bane to wear him down before Bane himself "breaks" him. Batman later defeats Croc in a one-on-one fight in the sewers, crushing a cylinder of knock-out gas against the underside of his nose to disable him. Croc is then arrested and held in Blackgate Prison with the other Arkham escapees until the asylum can be rebuilt.
^Manning, Matthew K.; Dolan, Hannah, ed. (2010). "1980s". DC Comics Year By Year A Visual Chronicle. Dorling Kindersley. p. 200. ISBN978-0-7566-6742-9. "Killer Croc made his mysterious debut in the pages of Detective Comics #523, written by Gerry Conway, with art by Gene Colan." "Croc would soon become a major player in Gotham's underworld."
^Game Informer features a two-page gallery of the many heroes and villains who appear in the game with a picture for each character and a descriptive paragraph. See "LEGO Batman: Character Gallery," Game Informer 186 (October 2008): 93.