An extensive list and short descriptions of the characters mentioned in the 4 Harry Potter Books.
 

 A-C

Abbott, Hannah: A Hufflepuff in Harry's year.
Abercrombie, Euan: A Gryffindor student
Ackerly, Stewart: A Ravenclaw student.
Agrippa: A character on a chocolate frog card.
Alberic: A character on a chocolate frog card.
Andromeda: Tonks' mother, Sirius' favorite cousin, married Ted Tonks (a muggle)
Aragog: Was fed and raised by Hagrid when he was a child. Now is the leader of the giant spiders in the Forbidden Forest.
Avery: A death eater
Baddock, Malcolm: A Slytherin student.
Bagman, Ludo: The former Wimbourne wasps beater who was accused of being a death eater and commentated at the Quidditch World Cup. He lost all his money on bets and couldn't pay his debts.
Bagman, Otto: Ludo's brother.
Bagnold, Millicent: Minister of Magic before Fudge
Bagman, Otto: Ludo's brother.
Bagshot, Bathilda: Author of "A History of Magic".
Bane: A centaur. Harry meets him in the Forbidden Forest.
Bell, Katie: One of the chasers for Gryffindor.
Prof. Binns: The History of Magic teacher. He is the only teacher that is a ghost.
Black, Mrs: Sirius' mum, has a screeching portrait
Black, Regulus: Sirius' brother, a Death Eater who was killed by Voldemort
Black, Sirius: Harry's godfather who was wrongly accused of killing Peter Pettigrew and twelve other muggles. He spent thirteen years in Azkaban.
Bletchley: The keeper for the Slytherin quidditch team.
Bloody Baron: The Slytherin ghost. Nobody knows how he got all of the blood stains on him.
Boardman, Stubby: the Quibbler says he is Sirius, lead singer of the Hobgoblins
Bole: Book 4 Slytherin beater
Bones: A Wizard family that Voldemort killed.
Bones, Amelia: Head of Dept. of Magical Law Enforcement, a fair person, Susan's aunt
Bones, Edgar: member of the original OotP, Amelia's brother, he died
Bones, Susan: A Hufflepuff in Harry's year who's parents were killed by Voldemort.
Boot, Terry: A Ravenclaw in Harry's year.
Bott, Bertie: The guy that invented "Bertie Bott's Every Flavor Beans".
Branstone, Eleanor: A Hufflepuff student.
Bryce, Frank: The Riddle's gardener who was murdered by Lord Voldemort.
Brocklehurst, Mandy: A Ravenclaw in Harry's year.
Brown, Lavender: A Gryffindor in Harry's year.
Buckbeak: The hippogriff who bit Malfoy and was beheaded for being "savage." Was saved when Hermione and Harry went back in time to saveSirius and Buckbeak.
Bungy: A muggle water skier
Bulstrode, Millicent: A Slytherin in Harry's year. Hermione turned into her cat, when drinking the polyjuice potion in there 2nd Year.
Cauldwell, Owen: A Hufflepuff student.
Chang, Cho: Harry's crush who is a year older and is also seeker for the Ravenclaw quidditch team.
Circe: A character on a chocolate frog card.
Cliodna: A character on a chocolate frog card.
Corner, Michael: Ginny's boyfriend
Crabbe, Vincent: One of Draco Malfoy's henchmen. In one word, a brute.
Creevey, Colin: Worships Harry. He was petrified when the Chamber of Secrets was opened.
Creevey, Dennis: Colin's younger brother.
Crockford, Doris: A woman at the Leaky Cauldron that kept lining up to shake Harry's hand.
Crookshanks: Hermione's big hairy orange/brown cat who was accused of killing Scabbers and helped Sirius get into Hogwarts.
Crouch, Bartemius: The deceased head of "International Magical Cooperation".
Crouch, Bartemius Jr.: Tortured Mr. and Mrs. Longbottom and escaped from Azkaban only to lock up then impersonate Alastor Moody throughout Harry's 4th year at Hogwarts. Received the dementor's kiss, under the order of Cornelius Fudge
 

D-G

Dawlish: a Fudge follower
Dennis: He is in Dudley's little gang of big, stupid, bullies.
Dearborn, Caradoc: member of the original OotP, vanished
Derrick: Book 4 Slytherin beater
Diggle, Dedalus: McGonagall suspects that he set off fireworks the day Voldemort fell. He also meets Harry at the Leaky Cauldron.
Doge, Elphias: Member of the OotP, a wheezy voiced wizard
Dorkins, Mary: A muggle news reporter
Dolohov, Antonin: a Death Eater, killed the Prewetts
Dumbledore, Albus: He is the headmaster at Hogwarts and one of the most respected wizards in the world.
Dumbledore, Aberforth: Member of the original OotP, Albus' brother
Dursley, Dudley: Harry's fat cousin who is a mean, spoiled, bully.
Dursley, Marge: Sister of Vernon Dursley, she hates Harry, maybe even more then the other Dursleys. She breeds dogs, and her favorite dog is named Ripper.
Dursley, Petunia: Harry's long necked aunt who spends much of her time spying on the perfectly normal neighbors.
Dursley, Vernon: Harry's big beefy, mean, uncle with hardly any neck who is the president of a drill company named Grunning's.
Delacour, Fleur: The Beauxbatons school champion.
Delacour, Gabrielle: Fleur's little eight year-old sister whom Harry rescued from the depth's of the lake during hte second task.
Delaney Podmore, Patrick: The leader of the headless hunt in which Nearly Headless Nick could not participate in.
Derwent, Dilys: Hogwarts headmaster & St. Mungo's Healer
Diggory, Amos: Cedric's father who is the head of the Department of Magical Transportation in the ministry.
Diggory, Cedric: One of the Hogwart's school champions who was killed by Lord Voldemort. He was in Hufflepuff and was captain and seeker of the Hufflepuff quidditch team.
Dobbs, Emma: A Hogwarts student.
Dobby: The Malfoy's house elf, who was set free by Harry, he now works at Hogwarts.
Edgecombe, Madam: Marietta's mom, works in the Dept. of Magical Transportation: Floo Office
Elladora: Sirius' aunt, beheaded old house elves
Emeric the Evil: was mixed up with Uric the Oddball in History of Magic.
Errol: The Weasley's old beat up owl.
Evans, Mark: A boy Dudley beats up
Everard: A great Hogwarts headmaster
Fat Friar: The Hufflepuff house resident ghost.
Fawkes: Dumbledore's pet phoenix who saved Harry's life in the Chamber of Secrets.
Fenwick, Bengy: member of the original OotP, they only found bits of him
Filch, Argus: The Hogwarts caretaker who is a squib and is constantly raging a war againt the students.
Finnigan, Seamus: One of Harry's fellow Gryffindor friends.
Fletcher, Mundungus: He tried to put a hex on Arthur Weasley when he had his back turns. Dumbledore also mentions him as one of the "old crowd".
Fortescue: previous Hogwarts headmaster
Goshawk, Miranda: Author of "The Standard book of Spells, Grade 2."
Granger, Hermione: A very clever Gryffindor and Harry's and Ron's best friend.
Grawp: Hagrid's half-brother
Grogg, Elfida: someone in a portrait
Grubbly-Plank: Care of Magical Creatures professor
Gudgeon, Gladys: fan of Lockhart
 

H-K

Hagrid, Ruebus: Hogwarts gamekeeper, Harry, Hermione and Ron's friend. Teaches "Care of Magical Creatures" at Hogwarts.
Hedwig: Harry's devoted and faithful owl.
Hengist of Woodcroft: Chocolate frog card character.
Hermes: Percy's screech owl.
Higgs, Terrence: The Slytherin quidditch team's seeker before Malfoy.
Hooch, Madam: The quidditch teacher at Hogwarts.
Hopkirk, Mafalda: Witch from the Improper Use of magic Office. She sends Harry a warning after Dobby uses a Hover charm.
Hufflepuff, Helga: One of the four powerful witches and wizards that founded Hogwarts. Hufflepuff house is named after her.
Humberto, The Great: Person on a show, Dudley is mad that he missed when the Dursleys and Harry are running from all of the letters.
Imago, Inigo: author of "The Dream Oracle"
Jigger, Arsenius: Author of "Magical Drafts and Potions."
Johnson, Angelina: Gryffindor student and chaser.
Jones, Hestia: Member of the OotP, a pink-cheeked, black-haired witch
Jordan, Lee: The Weasley twins' friend. Gryffindor student and announcer for the quidditch matches.
Jugson, Nott: Death Eater
Karkaroff, Igor: Durmstrang Institute headmaster. Former death eater now on the run from Lord Voldemort.
Karkus: Giant king (Gurg)
Kirke, Andrew: Gryffindor beaters (Book 5)
Kreatcher: the Black's house elf
Krum, Viktor: Bulgarian National quidditch team's seeker. Student at Durmstrang, dated Hermione at the Yule Ball.
 

L-O

Lestrange, Bellatrix: Sirius' cousin, married Rodolphus Lestrange
Lestrange, Rabastan: Rodolphus' brother
Lestrange, Rodolphus: married Bellatrix Black
Lockhart, Gilderoy: Former Defense Against the Dark Arts teacher. Lost his memory. A Wizard celebrity.
Longbottom, Algie: Neville's great uncle .
Longbottom, Alice: Neville's mother who was tortured by the Lestranges
Longbottom, Enid: Neville's great aunt.
Longbottom, Frank: Neville's father who was tortured by Bartemius Crouch Jr. and lost his memory.
Longbottom, Neville: An extremely forgetful Gryffindor student.
Lovegood, Luna: an eccentric Ravenclaw
Lupin, Remus: Former Defense Against the Dark Arts teacher. Is a werewolf.
MacDougal, Morag: Student at Hogwarts mentioned in the sorting.
MacMillan, Ernie: Hufflepuff student who was petrified when the Chamber of Secrets was opened.
Malfoy, Draco: Harry's arch-nemesis. A Slytherin student and seeker.
Malfoy, Lucius: Draco's father, is a Death Eater...could be Voldemorts right-hand man.
Malfoy, Narcissa: Draco's pale-faced mother.
Malkin, Madam: Owns robe shop.
Mason, Mr. and Mrs.: A rich builder and wife who come to a dinner party at the Dursley's on Harry's twelfth birthday.
Marchbanks, Griselda: on the Wizengamot, Dumbledore supporter, O.W.L. examiner, Neville's gran's friend
Marsh, Madam: Got sick on the Knight Bus
Maxine, Olympe: Half-giant headmistress of Beauxbatons Academy, claims she is Big-Boned...Hagrid has a crush on her.
McGonagall, Minerva: The strict Transfiguration teacher. Is Head of Gryffindor house and Deputy Headmistress of Hogwarts.
McGuffin, Jim: Muggle weatherman.
McKinnons: A Family killed by Voldemort
Meadowes, Dorcas: member of the original OotP, killed by Voldemort
Meliflua, Araminta: Sirius' mother's cousin, made Muggle hunting legal
Merlin: Character on Chocolate Frog card.
Mimsey-Porpington, Sir Nicholas de: Nearly Headless Nick's real name, The Gryffindor house resident ghost. His head is held on by a miniscule piece of flesh. Been Dead for over 500 Years.
Moaning Myrtle: Unhappy girl ghost that haunts the upstairs girls' bathroom. Was killed by the Basilisk in 1942.
Montague: Slytherin Quidditch captain, Book 5
Moody, Alastor: Former Defense Against the Dark Arts teacher. Highly successful auror, was stunned and kept in a box throughout the entire schoolyear at Hogwarts while he was being impersonated by the late Bartemius Crouch Jr.
Moon: A Hogwarts student mentioned in sorting.
Moony: Remus Lupin's childhood nickname.
Morgana: Character on Chocolate Frog card.
Munch, Eric: Ministry of Magic watchwizard
Mrs. Norris: Filch's cat that stalks the castle looking for any rule-breaking.
Nearly Headless Nick: The Gryffindor house resident ghost. His head is held on by a miniscule piece of flesh. Been Dead for over 500 Years.
Nigellus, Phineas: Sirius' great, great, grandfather, a Hogwarts Headmaster
Norbert the Norwegian Ridgeback: Hagrid's pet dragon.
Nott: A Student at Hogwarts mentioned in the sorting.
Ogden, Tiberius: On the Wizengamot
Ollivander: Owns the wand shop in Diagon Ally
 

P-S

Padfoot: Sirius Black's childhood Hogwarts nickname.
Parkinson, Pansy: A Slytherin girl with a face like a pug.
Peeves: A poltergeist who loves to get students in trouble. The only person who can control him is the Bloody Baron.
Perkins: A timid, old wizard
Pigwidgeon: Ron's overexcited tiny owl that was given to him by Sirius.
Pince, Madam: The irritable Hogwarts librarian.
Polkiss, Piers: Dudley's friend. He goes to the zoo with the Dursleys and Harry.
Podmore, Sturgis: Member of the OotP, a square jawed wizard w/ straw colored hair
Pomfrey, Poppy: The Hogwarts school nurse. Harry sees her quite often.
Potter, Harry: "the boy who lived". Harry lives with his aunt, uncle, and cousin that despise him before learning that he is a wizard. He goes to the Hogwarts School of Witchcraft and Wizardry.
Potter, James: Harry's father who was killed by Lord Voldemort.
Potter, Lily: Harry's mother who was also killed by Lord Voldemort.
Prentice, Mr: Mrs. Figg's cat?
Prewett, Gideon & Fabian: members of the original OotP, killed by five Death Eaters
Prongs: James Potter's childhood nickname.
Ptolemy: Character on Chocolate Frog card. Ron doesn't have this one.
Pucey, Adrian: A Slytherin chaser and student.
Purkiss, Doris: thinks Black is innocent and that Stubby Boardman is Sirius
Puddifoot, Madam: runs a teashop in Hogsmeade
Quirrel: Former Defense Against the Dark Arts teacher who is now dead.
Rackharow, Urquhart: inventor of the Entrail-Expelling Curse (1612-1697)
Ravenclaw, Rowena: One of the four great wizards and witches that founded Hogwarts. Ravenclaw house is named after her.
Riddle, Tom: a.k.a. Lord Voldemort. Tried to murder Harry in the Chamber of Secrets.
Ripper: Aunt Marge's dog who pines when she's away, chased Harry up a tree years ago.
Ronan: A centaur in the Forbidden Forest.
Ryan, Barry: Ireland's Quidditch keeper
Rookwood, Augustus: leaked Ministry secrets to Voldemort, an Unspeakable
Scabbers: a.k.a Peter Pettigrew. Pretended to be Ron's rat for thirteen years.
Scamander, Newt: Author of "Fantastic Beasts and Where to Find Them"
Scrimgeour: Someone who is against the OotP
Shackelbolt, Kingsley: Member of the OotP, a tall black wizard
Skeeter, Rita: Daily Prophet writer who writes horrible lies about people including Harry, Hermione and Hagrid.
Slinkard, Wilbert: an author
Sloper, Jack: Gryffindor beater (Book 5)
Slytherin, Salazar: One of the four whiches and wizards who founded Hogwarts. Slytherin house is named after him. He created the Chamber of Secrets.
Snape, Severus: The greasy haired potions teacher whom is head of Slytherin house and hates Harry.
Smethwyck, Hippocrates: Healer in Charge at St. Mungo's
Smith, Zacharias: blonde-haired member of the Hufflepuff Quidditch team
Spinnet, Alicia: A Gryffindor chaser and student.
Spore, Phyllida: Author of "One Thousand Magical Herbs and Fungi."
Sprout, Proffesor: Herbology teacher and head of Hufflepuff house.
Stimpson, Patricia: Had O.W.L. breakdowns, in Fred/George's year
Strout, Miriam: St. Mungo Healer
Switch, Emeric: Author of "A Beginners' Guide to Transfiguration."
 

T-Z

Ted: Muggle news reporter.
Thomas, Dean: A tall, black Gryffindor student who is a very good drawer.
Tibbles, Mr: Mrs. Figg's cat
Tom: Bartender at the Leaky Cauldron.
Tofty: O.W.L. examiner
Tonks, Nymphadora: Member of the Order of the Phoenix, an Auror, a metamorphmagus
Tonks, Ted: Nymphadora's muggle father, married Andromeda
Towler, Kenneth: Had O.W.L. breakdowns, in Fred/George's year
Trelawney, Sibyll: The misty eyed Divination teacher with huge glasses.
Trevor: The name of Neville's toad, Trevor seems to always be missing.
Trimble, Quentin: Author of "The Dark Forces: A Guide ot Self Protection."
Turpin, Lisa: A Ravenclaw student.
Umbridge, Dolores Jane: Senior Undersecretary to Minister, DADA teacher (Book 5)
Uric the Oddball: was mixed up with Emeric the Evil in History of Magic.
Vablatsky, Cassandra: Author of "Unfogging the Future."
Vance, Emmeline: Member of the OotP, a stately witch
Viridian, Vindictus: Author of "Curses and Countercurses."
Voldemort: a.k.a Tom Riddle, The dark lord. Most wizards refer to him as "you-know-who" or "he-who-must-not-be-named".
Waffling, Adalbert: Author of "A Magical Theory."
Warbeck, Celectina: A popular singing sorceress.
Warrington: Slytherin beater
Weasley, Arthur: Ron's father who is head of the "Misuse of Muggle Artifacts Office" in the ministry.
Weasley, Bill: The eldest Weasley brother. Is a charm-breaker at Gringotts. Was Head Boy at Hogwarts, when he attended there.
Weasley, Charlie: The second eldest Weasley brother. He breeds dragons in Romania, he was the Gryffindor Quiddith Captain, when he was at Hogwarts.
Weasley, Fred and George: Ron's two year older twins who are funny and beaters for the Gryffindor quidditch team.
Weasley, Ginny: The youngest Weasley. Has a crush on Harry.
Weasley, Molly: The mother of all of the Weasley kids.
Weasley, Percy: The strict rule-abiding Weasley who now works in the Ministry.
Weasley, Ron: Harry's best friend at Hogwarts. Like his five older brothers, he is in Gryffindor house.
Widdershin, Willy: made regurgitating toilets
Winky: Barty Crouch's house elf that was sacked at the Quidditch World Cup and now works at Hogwarts.
Wood, Oliver: The former Gryffindor quidditch team's captain who now is a reserve keeper for Puddlemore United.
Wormtail: Peter Pettigrew's childhood Hogwarts nickname.
Yvonne: Aunt Petunia's friend that is vacationing in Majorca during the first book.
Zabini, Blaise: A Slytherin girl.
Zamojski, Ladislaw: Poland's Quidditch chaser