Castle is an American crime drama television series, which premiered on ABC on March 9, 2009. The series is produced jointly by Beacon Pictures and ABC Studios. Created by Andrew W. Marlowe, it primarily traces the lives of Richard Castle (Nathan Fillion), a best-selling mystery novelist, and Kate Beckett (Stana Katic), an NYPD homicide detective, as they solve various unusual crimes in New York City. Detective Beckett is initially infuriated at the thought of working with a writer and goes to great lengths to keep him out of her way. However, the two soon start developing feelings for each other. The overarching plot of the series focuses on the romance between the two lead characters, as well as the murder of Beckett's mother.
Castle follows Nathan Fillion as Richard Castle, a famous mystery novelist who has killed off the main character in his book series and has writer's block. He is brought in by the NYPD for questioning regarding a copy-cat murder based on one of his novels. He is intrigued by this new window into crime and murder, and uses his connection with the Mayor to charm his way into shadowing Detective Kate Beckett, played by Stana Katic. Castle decides to use Beckett as the model for Nikki Heat, the main character of his next book series. Beckett, an avid reader of Castle's books, initially disapproves of having Castle shadow her on her cases, but later warms up and recognizes Castle as a useful resource in her team's investigations.
Nathan Fillion as Richard Edgar Castle/Richard Alexander Rodgers, a best-selling mystery writer. Plagued with writer's block after killing off his popular lead character, Derrick Storm, whom he no longer found inspiring, Castle found himself involved in the case of a copy-cat killer recreating murder scenes from his novels. He discovers a new source of inspiration in Kate Beckett, the detective leading the investigation, so uses his friendship with the mayor of New York to become involved in her investigations as a civilian consultant. He regularly uses his knowledge and talent to help solve murders, usually by taking evidence and assembling it into a narrative to explain their current case. He is twice-divorced and shares an apartment with his daughter and his mother. Earlier seasons of the show depict him as an immature womanizer; however, later seasons show a more mature and sensible side of him albeit only slightly. His close working relationship with Beckett results in him falling in love with her. He proposes at the end of the fifth season, and the two become engaged.
Stana Katic as Detective Katherine Houghton "Kate" Beckett, a homicide detective with the NYPD's 12th Precinct. Beckett is a first-class investigator who has gained a reputation for being intrigued by unusual cases. She joined the force after her mother was murdered in an unsolved case. After meeting Beckett, Castle is inspired to begin a new series of novels about a female NYPD detective named Nikki Heat, clearly based on Beckett. Initially cold and hard towards Castle, she soon warms up to him and eventually falls in love with him. In the fourth-season finale, Beckett resigns from the NYPD after she and Det. Esposito hide vital information regarding a case from Captain Gates, but later reneges on this and is allowed to return after she serves her suspension. She also briefly worked as a Special Investigator for the Attorney General before returning to the NYPD. In the first episodes of season five, it became clear that Kate and Castle are in an intimate relationship, and the two become engaged at the start of the sixth season.
Jon Huertas as Detective Javier "Javi"/"Espo" Esposito, a former Army Special Forces soldier who now works in the homicide division as part of Beckett's team. He is always ready with a sardonic comment to keep Beckett on her toes and enjoys the way Castle riles her. He recognizes Castle and Beckett's attraction from the start and sometimes advises Beckett on her relation to Castle. He and Kevin Ryan are close friends, even though they constantly argue about obscure facts. He had a brief relationship with Dr. Lanie Parish in the third season, which ended with things being awkward between them making them unable to work around each other for some time. He was suspended from the NYPD for hiding vital information from Captain Gates in a case concerning Beckett's well-being. In that case, he felt betrayed by his partner, Det. Kevin Ryan. He has since been reinstated on the force and has reconciled with Ryan.
Seamus Dever as Detective Kevin Ryan, a former Narcotics detective who also works as part of Beckett's team. He and Esposito regularly tease Beckett, but they are also protective of her. The character was a late addition to the show as the original presentation pilot was only 37 minutes long. Ryan marries his girlfriend, Jenny O'Malley, in season four. In the final episode of season four, Ryan fails to support Beckett and his partner Esposito, which jeopardizes his partnership with the two of them though they reconcile later. In season five he is revealed to have worked undercover in the Irish mob. In season six, Jenny gives birth to their daughter.
Tamala Jones as Dr. Lanie Parish, a medical examiner with an upbeat outlook. She is a friend of Beckett and is one of the few people Beckett can talk to easily and without reservation. Parish notices the personal connection between Beckett and Castle and urges her to act on it. In the third season, Lanie and Esposito began a relationship they believed was secret, though the other main characters were aware of it. They later broke up, making it awkward for them to work together for a time, but have since reconciled.
Ruben Santiago-Hudson as Captain Roy Montgomery (Season 1–3), Beckett's boss and Captain of the 12th Precinct. Montgomery appreciates Beckett's determination and diligence but maintains a close watch to make sure the investigations go smoothly. He is amused by how much Castle annoys Beckett but also appreciates how effectively the two work together. At the end of the third season, he is killed after staging a trap to capture a hired killer involved in the conspiracy that killed Beckett's mother. In the sixth-season episode "Veritas", Beckett recalls Montgomery telling her, before she became a detective, to look through her mother's belongings for a clue in her murder. It is revealed that he recorded an audiotape implicating Bracken.
Molly Quinn as Alexis Castle, Castle's teenage daughter by his first wife Meredith. Alexis is unusually intelligent for her age, and is often more mature and responsible than her father. She is very bright and enjoys school. A running gag in the series has her begging Castle to force her to study and do her homework instead of "fun" activities like parties and overnight trips. Her social and interpersonal issues often parallel some aspect of the case Castle and Beckett are investigating, and Castle sometimes asks her opinion on a killer's motivation.
Susan Sullivan as Martha Rodgers, an actress on and off Broadway and Castle's mother. She lives with him and Alexis after an ex-husband ran off with her life savings. She helps her son through the difficulties of raising a teenage girl (even one as mature as Alexis) but also has an active social life of her own. She is free-spirited and often gives Castle valuable advice regarding Beckett.
Penny Johnson Jerald as Captain Victoria Gates (Season 4–), Captain Montgomery's replacement. Formerly with Internal Affairs, Captain Gates (referred to by some as "Iron Gates") is more interested in career advancement, and takes a dimmer view than her predecessor of the Beckett-Castle dynamic. Strict and unforgiving, she loathes Castle's presence at the precinct regarding him as an unprofessional, distracting and juvenile presence who interferes with the way she would prefer to run things. As the series progresses she comes to tolerate Castle, and even grudgingly accept that he is useful for solving cases. Though her outright hostility fades, she is nonetheless strictly by the book, and still willing to beat Castle with it when needed.
Monet Mazur as Gina Cowell, Castle's publisher and second ex-wife. Their professional relationship has been known to overshadow their personal one, causing conflict.
Victor Webster as Dr. Josh Davidson, Beckett's motorcycle-riding, cardiac surgeon ex-boyfriend whom Castle repeatedly refers to as "motorcycle boy" and "doctor motorcycle boy".
Ken Baumann as Ashley, Alexis' steady boyfriend. Alexis broke up with Ashley after her father and grandmother were involved in a hostage situation and Ashley was nowhere to be found to help her through it.
Bailey Chase as Will Sorenson, an FBI agent and Beckett's ex-boyfriend who immediately recognizes Beckett's attraction to Castle.
Jason Beghe as Mike Royce, Beckett's former training officer who retired to become a bounty hunter. He is killed in "To Love and Die in L.A.".
Michael Dorn as Dr. Carver Burke, a psychiatrist who helps Beckett overcome her shooting and also deal with her various hidden emotions.
Geoff Pierson as Mr. Smith, a friend of Captain Montgomery holding evidence that keeps the murderer of Beckett's mother away from Beckett; Smith occasionally acts through Castle to protect Beckett. He appeared to have been killed in "After the Storm," but in the episode "Veritas," it is revealed that he faked his death in order to operate in the shadows.
Darby Stanchfield as Meredith, an actress who is Castle's first wife, and Alexis's mother. She is regularly portrayed as self-centered and dramatic.
Michael Mosley as Jerry Tyson/the Triple Killer (3XK), a methodical and meticulous serial killer who returns to New York every few years to terrorize the city. After being identified by Castle, Tyson turns his attentions on the 12th Precinct, variously targeting members of Beckett's team. He is shot and presumed to be dead in "Probable Cause", though Castle expresses doubts about it. It is suggested that he is still alive during the events of "Disciple", but the episode also explores the implications of his death, which leave Castle and Beckett disturbed.
Jack Coleman as William Bracken, a popular and charismatic Senator representing the State of New York with ambitions of one day becoming President. He presents himself as an honest man looking out for special interests, but is directly responsible for the events of the series' main narrative arc and serves as the primary antagonist.
James Brolin as a CIA deep-cover operative whose real name remains unknown. Instead he has gone by aliases such as "Jackson Hunt" and "Anderson Cross". He is treated as a near-mythical figure in the intelligence community. He is revealed to be Castle's father in the two-part episode "Target" and "Hunt". Despite the loneliness of his profession, he has maintained indirect contact with his son.
Maya Stojan as Tory Ellis, an NYPD Tech officer who assists on Beckett's cases.
Phil LaMarr as Dr. Holloway, a psychiatrist who evaluates the metal stability of suspects.
Myko Oliver as Pi, Alexis's boyfriend at the beginning of season 6, in which she shared an apartment with.
Real-life writers Stephen J. Cannell, James Patterson, Dennis Lehane, and Michael Connelly appear as themselves during periodic games of poker at Castle's apartment. Typically, they discuss Castle and Beckett's current case and tease Castle about his involvement with Beckett. On September 30, 2010, Cannell died in real life. The characters kept an empty chair at the poker table in his honor for a year.
Castle premiered as a midseason replacement on ABC on March 9, 2009. ABC renewed Castle for a second season with an initial order of 13 episodes; ABC later extended the order to 22, then 24 episodes. The second season premiered on Monday, September 21, 2009. In March 2010, ABC renewed Castle for a third, 22 episode season, which began on September 20, 2010. On November 11, 2010, ABC extended the episode order to 24. On January 10, 2011, ABC announced Castle had been renewed for a fourth season for 22 episodes. Season four premiered on September 19, 2011. On December 8, 2011, ABC ordered an additional episode bringing season 4 up to 23 episodes. On May 10, 2012, Castle was renewed for a fifth season by ABC, which started on Monday September 24, 2012. Two additional episodes were ordered on October 19, 2012 and February 5, 2013, respectively. This brings season 5 up to a total of 24 episodes. On May 10, 2013, ABC announced via Twitter that Castle had been renewed for a sixth season. On May 8, 2014, ABC renewed the series for a seventh season, which is due to premiere on September 29, 2014. 
The Season 2 episode "Boom!" (the finale of a two-part episode featuring Dana Delany) not only attracted the highest audience of the show's run (14.5 million viewers), but was also the highest rated show on ABC in its time slot in 14 years.
Character Commentary (Need To Know episode) with Detectives Javier Esposito and Kevin Ryan, Castle Karaoke, Castle in a Day with Stana Katic, A Few of Our Favorite Things (including debut an unaired Castle and Kate moment from the season 4 finale), audio commentaries, deleted scenes, and bloopers.
In June 2011, TNT acquired exclusive cable rights from Disney-ABC Domestic Television to air the first two seasons of Castle beginning in the summer of 2012. In advance of the series' fourth season, TNT broadcast an eight-hour marathon of episodes on September 15, 2011, including five from season 3.Castle began airing on TNT every Wednesday beginning September 26, 2012.Castle also began airing in broadcast syndication on weekends beginning September 29, 2012.
In the series, Castle writes a novel titled Heat Wave. As a tie-in, ABC and sister publisher Hyperion Books released that novel as a real book (ISBN 978-1-4013-2382-0) with "Richard Castle" as the author. It is entirely in character from the dedication to the acknowledgments, although the latter mentions the principal cast and the show's creators by first name. ABC released the first half of the novel in weekly increments on their website. The complete novel was published in September 2009 as a hardcover, debuting at No. 26 on The New York Times Best Seller list. In its fourth week on the list, Heat Wave broke into the top 10 at #6.Heat Wave was released in paperback (ISBN 978-1-4013-1040-0) on July 27, 2010 and debuted at No. 34 on The New York Times bestseller Paperback Mass-Market list. It once again appeared on The New York Times bestseller list on May 27, 2012 at #19.
Naked Heat (ISBN 978-1-4013-2402-5), the sequel to Heat Wave, was released on September 28, 2010.Naked Heat debuted at No. 7 on the New York Times Best Seller list. As they did with Heat Wave, ABC released a series of the early chapters online as a promotional tool.
The season three finale introduced a graphic novel based on Castle's previous novel character, Derrick Storm. Castle: Richard Castle's Deadly Storm was published by Marvel Comics on September 28, 2011. It debuted at No. 3 on The New York Times bestseller list on October 16, 2011.
In February 2012, Hyperion announced three e-book novellas to Richard Castle's famous Derrick Storm series. The first novella of the series, A Brewing Storm, was released in digital media on May 1, 2012. It debuted at No. 13 on The New York Times E-Book Fiction bestseller list, as well as No. 18 on the New York Times Combine Prints & E-book Fiction list on May 20, 2012.
On July 3, 2012, the second novella of the new Derrick Storm books, A Raging Storm, was released in e-book format. It landed on The New York Times bestseller e-books list at #19 and at No. 31 for the combined Prints & E-book list, both on July 22, 2012.
The final Derrick Storm novella, A Bloody Storm, was released on August 7, 2012. It debuted on the New York Times bestseller e-books list at #20 and at #34 on the combined Prints & E-book list on August 26, 2012.