Regulus Arcturus Black – Brother of Sirius Black, a Death Eater who turned against Lord Voldemort and paid for it with his life.
Sirius Black – Harry Potter's godfather, Gryffindor student at Hogwarts, Animagus, Marauder, disowned for running away from home to live with the Potter family, member of the Order of the Phoenix, killed by his cousin Bellatrix Lestrange
Vincent Crabbe – Slytherin student in Harry's year, son of Death Eater, Slytherin Quidditch team Beater, member of the Inquisitorial Squad
Colin Creevey – Muggle-born Gryffindor student one year below Harry, brother of Dennis Creevey, member of Dumbledore's Army, killed during the Battle of Hogwarts, after sneaking away from the younger evacuated students in the seventh book
Dennis Creevey – Muggle-born Gryffindor student three years below Harry, brother of Colin Creevey, member of Dumbledore's Army
Dirk Cresswell – Muggle-born Head of the Goblin Liaison Office, went on the run in Deathly Hallows with fellow muggle-born Ted Tonks, Dean Thomas and goblins Gornuk and Griphook, killed by snatchers along with Ted and Gornuk
Albus Dumbledore – Hogwarts Headmaster in Harry Potter's time, Transfiguration professor in Tom Riddle's time, founder of the Order of the Phoenix, killed by Severus Snape.
Ariana Dumbledore – Sister of Aberforth and Albus Dumbledore, magically unstable after an assault by muggle boys when she was little, killed accidentally in childhood by either Albus, Aberforth or Gellert Grindelwald.
Kendra Dumbledore – Muggleborn mother of Albus, Aberforth and Ariana Dumbledore, killed accidentally by one of Ariana's outbursts.
Percival Dumbledore – Father of Albus, Aberforth and Ariana Dumbledore, died in Azkaban after he took vengeance on some muggle boys who assaulted his daughter.
Dudley Dursley – Muggle son of Vernon Dursley and Petunia Evans, first cousin of Harry Potter
Cornelius Fudge – Minister for Magic from sometime during the 1980s until summer of 1996 when he was forced to resign.
Marvolo Gaunt – Pure-blood father of Merope and Morfin Gaunt, grandfather of Tom Marvolo Riddle, descendant of Salazar Slytherin and Cadmus Peverell
Merope Gaunt – Daughter of Marvolo Gaunt, sister of Morfin Gaunt, wife of Tom Riddle Sr, mother of Tom Marvolo Riddle/Lord Voldemort, died during childbirth, named for Merope, one of the Pleiades, who married a mortal
Morfin Gaunt – Son of Marvolo Gaunt, framed by nephew Tom Riddle for Muggle killings, died in Azkaban
Viktor Krum – Durmstrang student, Bulgarian Quidditch Seeker, participated in the Triwizard Tournament
Bellatrix Lestrange (née Black) – Death Eater, sister of Narcissa Malfoy and Andromeda Tonks, cousin of Sirius and Regulus Black, she tortured Frank and Alice Longbottom into insanity with husband Rodolphus, killed Sirius Black, Nymphadora Tonks, and Dobby. Killed by Molly Weasley.
Rodolphus Lestrange – Death Eater, brother of Rabastan Lestrange, husband of Bellatrix Lestrange, uncle of Nymphadora Lupin (née Tonks) and Draco Malfoy, tortured Frank and Alice Longbottom into insanity with wife Bellatrix
Gilderoy Lockhart – Fraudulent author, Defence Against the Dark Arts teacher, lost memory because of a backfiring memory spell he attempted with Ron's broken wand on Harry and Ron, permanently resides at St. Mungo's
Alice Longbottom – Wife of Frank Longbottom, mother of Neville Longbottom, member of the original Order of the Phoenix, Auror, tortured into insanity by Bellatrix Lestrange along with her husband
Frank Longbottom – Father of Neville Longbottom, son of Augusta Longbottom, husband of Alice Longbottom, member of the original Order of the Phoenix, Auror, tortured into insanity by Bellatrix Lestrange along with his wife.
Neville Longbottom – Gryffindor student in Harry's year, member of Dumbledore's Army, son of Aurors Frank and Alice Longbottom, husband of Hannah Abbott, great-nephew of great-aunt Enid and great-uncle Algie.
Luna Lovegood – Ravenclaw student one year below Harry, member of Dumbledore's Army, daughter of Xenophilius Lovegood
Remus Lupin – Gryffindor student before Harry's time, Marauder, friend of James Potter, werewolf, Professor of Defence Against the Dark Arts in Harry's third year, member of the Order of the Phoenix, husband of Nymphadora Lupin (née Tonks) and father of Teddy Remus Lupin, killed in the Deathly Hallows by Antonin Dolohov
Teddy Lupin – Son of Remus Lupin and Nymphadora Lupin née Tonks, godson of Harry Potter
Draco Malfoy – Slytherin student in Harry's year, Slytherin Quidditch Seeker, school prefect, member of the Inquisitorial Squad
Lucius Malfoy – Draco Malfoy's father, an influential Death-Eater, and, early in the series, governor of Hogwarts
Narcissa Malfoy (née Black) – Lucius Malfoy's wife and Draco Malfoy's mother, sister of Bellatrix Lestrange and Andromeda Tonks
Theodore Nott - Slytherin student in the same year as Harry Potter. Nott is one of the few students who can see Thestrals, suggesting that he has witnessed a death at some point. His father, a death eater, having been described as an elderly widower.
Bob Ogden – Head of Magical Law Enforcement around the time Marvolo and Morfin Gaunt were arrested.
Tiberius Ogden – One of the examiners for O.W.L.s, has already been one of Albus Dumbledore's examiners around the turn of the century.
Dean Thomas – Gryffindor student in Harry's year, member of Dumbledore's Army, briefly Ginny Weasley's boyfriend, Gryffindor Quidditch Chaser.
Andromeda Tonks (née Black) – Daughter of Cygnus Black III and Druella Rosier, disowned for marrying Muggle-born Ted Tonks, sister of Bellatrix Lestrange and Narcissa Malfoy, mother of Nymphadora Lupin (née Tonks), grandmother of Teddy Remus Lupin, cousin of Sirius Orion and Regulus Arcturus Black, aunt of Draco Malfoy
Nymphadora Tonks – Daughter of Ted Tonks and Andromeda Black, disowned by the Black family for being half-blood, Auror, metamorphmagus, wife of Remus Lupin, mother of Teddy Remus Lupin, cousin of Draco Malfoy, killed by her aunt Bellatrix during the Battle of Hogwarts
Ted Tonks – Muggle-born husband of Andromeda Black, father of Nymphadora Lupin (née Tonks), grandfather of Teddy Remus Lupin, uncle of Draco Malfoy, killed by Death Eaters
Sybill Patricia Trelawney – Hogwarts Divination professor, predicted the prophecy that prompted Lord Voldemort to go after the Potters
Dolores Jane Umbridge – Senior Undersecretary to the Minister for Magic, Defence Against the Dark Arts professor, Hogwarts High Inquisitor, Headmistress of Hogwarts, eventually sent to Azkaban for crimes against Muggle-borns, claims relation to the pure-blood Selwyn family
Lord Voldemort – The antagonist of the series, murderer of Harry Potter's parents and many others.
Arthur Weasley – Ministry of Magic employee at the Misuse of Muggle Artifacts Office, husband of Molly Weasley, father of Bill, Charlie, Percy, Fred, George, Ron, and Ginny Weasley, member of the Order of the Phoenix
Bill Weasley – Oldest son of Arthur and Molly Weasley, Gringotts employee, husband of Fleur Delacour
Charlie Weasley – Second son of Arthur and Molly Weasley, formerly Gryffindor Quidditch Seeker and school prefect, member of the Order of the Phoenix, works with dragons in Romania
Fred Weasley – Son of Arthur and Molly Weasley and identical twin brother of George Weasley, member of Dumbledore's Army, Gryffindor Quidditch Beater, co-owner of Weasleys' Wizard Wheezes
George Weasley – Son of Arthur and Molly Weasley and identical twin brother of Fred Weasley, member of Dumbledore's Army, Gryffindor Quidditch Beater, co-owner of Weasleys' Wizard Wheezes
Ginny Weasley – Only daughter and youngest child of Arthur and Molly Weasley, Gryffindor student one year under Harry, Gryffindor Quidditch Seeker and Chaser, member of Dumbledore's Army.
Molly Weasley (née Prewett) – Wife of Arthur Weasley, mother of Bill, Charlie, Percy, Fred, George, Ron and Ginny Weasley, member of the Order of the Phoenix.
Percy Weasley – Third son of Arthur and Molly Weasley, Gryffindor prefect and Head Boy, Ministry of Magic employee, long estranged from his family before joining them against the Death Eaters in Deathly Hallows,
Ron Weasley – Harry's close friend, youngest Son of Arthur and Molly Weasley, Gryffindor Quidditch Keeper, school prefect, member of Dumbledore's Army.
Oliver Wood – Hogwarts student, Gryffindor Quidditch Keeper and captain, Keeper for Puddlemere United.
Yaxley – Death Eater, defeated by George Weasley and Lee Jordan
Blaise Zabini – Slytherin student in Harry's year, friends with Draco Malfoy.
Characters with no or unknown surname
Algie - Great-uncle of Neville Longbottom who tried to "startle" the magic out of him by endangering Neville's life repeatedly. Gave Neville his toad Trevor as a gift when Neville finally showed his first known bit of accidental magic.
Aragog – Acromantula belonging to Rubeus Hagrid, lives in the Forbidden Forest, dies in Half-Blood Prince.
Arnold - Ginny's pygmy puff she got before her fifth year, one of many bred by her twin brothers for sale in their shop.
The Bloody Baron – Slytherin House ghost, suitor and killer of Helena Ravenclaw, killed himself in remorse
Buckbeak (a.k.a. Witherwings) – Hippogriff belonging at various times to Rubeus Hagrid, Sirius Black, and Harry Potter
Sir Cadogan – Armoured and somewhat mad knight occupying a painting in Hogwarts
Crookshanks – Half-cat/half-kneazle belonging to Hermione Granger
Dobby– House-elf originally belonging to the Malfoy family, accidentally set free by Lucius Malfoy due to Harry's intervention in Chamber of Secrets. Killed by Bellatrix Lestrange while saving Harry Potter's life.
Kreacher – House-elf belonging to the Black family, and later Harry Potter. Though at first preferring to serve the pureblood line (including Regulus Black, Narcissa Malfoy, Bellatrix Lestrange, and Draco Malfoy), he eventually likes serving under Harry as he treats him better, giving him Regulus' locket as a gift.
Moaning Myrtle – Muggle-born Ravenclaw student during Tom Marvolo Riddle's time at Hogwarts, killed by the Basilisk in a girl's bathroom, which she continued to haunt (after she was banished while haunting Olive Hornby).
Scabbers – Pet rat belonging to Percy and later Ron Weasley; eventually revealed as unregistered Animagus Peter Pettigrew, used to be one of the group of friends "the Marauders" who nicknamed his rat-form "Wormtail".
Winky - A female house elf who originally belonged to Bartemius Crouch Sr., but was sacked by him when evidence emerged that she had used magic at The Quidditch World Cup. Currently working at Hogwarts School of Witchcraft and Wizardry
Wormtail - Nickname his friends gave Peter Pettigrew while he was still in school for his animagus-form of a rat. Preferred form of address instead of Pettigrew used (probably as a cruel reminder of the treason of his friends) by Voldemort.