The hero and protagonist, Harry is a twelve-year-old boy with messy hair and glasses who became famous within the wizard community by surviving the curse of a powerful wizard. Harry frequently finds himself entangled in dangerous adventures but he always lives to tell the tale. Harry's character represents good intentions, innocence, and the fantasies of childhood.
Ron is tall, red-haired, and from a respected but poor family. Ron is one of Harry's two best friends at Hogwarts. He is loyal to Harry, and belligerent to their enemy, Malfoy. Ron uses experience and a process of trial-and-error to solve most mysteries. Ron's character is often overshadowed by Harry's, but Ron always manages to succeed.
Hermione is always the top student in her class. She is clever and well-read. Most spells come easily to her and remain in her encyclopedic mind.. However, she is in principle a rule-follower, and so in this story she often alienates Harry and Ron by reporting or threatening to report them to Professor McGonagall, in cases such as Harry's gift of the Firebolt, or his possession and use of the Marauder's map.
Once a student who attended Hogwarts fifty years prior to Harry's time, Voldemort molded himself into the most powerful dark wizard the world has ever seen. Twelve years before, he killed Harry's parents and tried to kill Harry, only to have his curse backfire and render him powerless. It is generally believed that Sirius Black turned Harry's parents over to Voldemort, although in truth, Peter Pettigrew is guilty.
Lupin is the new Defense Against the Dark Arts teacher, and he is very competent and likeable. He teaches Harry how to defend himself against Dementors, but he is forced to leave Hogwarts at the end of the year on account of his being a werewolf. He is one of the creators of the Marauder's Map.
Once James Potter's best friend, now an escaped convict from the wizard prison Azkaban, Black is suspected to be the cause of twelve Muggle deaths as well as the indirect cause of the deaths of Harry's parents. He is a threat on the frontier of this story, one of the premier good wizards turned bad, although in the end he is revealed to be innocent in addition to being Harry's godfather. Also, Black is able to transform himself at will into Padfoot, a large black dog that Harry mistakes for the Grim. One of the creators of the Marauder's Map.
The gamekeeper at Hogwarts and a good friend of Harry's, Hagrid is a giant, hairy man with an inimitable accent, and he has a great liking for strange and dangerous creatures. In this book, he is the defender of Buckbeak, a hippogriff that is placed on trial for injuring Draco Malfoy.
The fourth in the group of friends that included James Potter, Sirius Black, and Remus Lupin, Pettigrew betrayed Lily and James, turning their whereabouts over the Voldemort, then blowing up a dozen Muggles, framing Black and turning himself into a rat so that he could escape. Another of the creators of the Marauder's Map. Disguised as Scabbers, he has lived many years as Ron's pet rat.
Dumbledore, the headmaster of Hogwarts, is a wise, powerful, elderly man with a long silver beard, and he is one of the most impressive characters Harry has ever met. He has a calm, secretive demeanor and is extremely intuitive, tolerant, and trustworthy.
The Divination Professor; an insect-like, rather dramatic women who loves predicting deaths but is not at all accurate in her predictions.
The head of Gryffindor House, a stern but deeply concerned witch, and a great aficionado of Quidditch.
The Potions teacher, and a slimy, ill-tempered man, Snape is the head of Slytherin House and gets great pleasure out of trying to get Harry into trouble.
A small, kind professor who teaches Charms.
A slimy, smirking, and snotty boy from Slytherin House, Malfoy is Harry's greatest Hogwarts nemesis (not counting Voldemort, who usually resides outside Hogwarts). Because his family is very wealthy and influential, Malfoy is able to use his father's power as an intimidation tactic, in this book when he tries to have Hagrid fired and Buckbeak executed.
Draco Malfoy's father, a mean, powerful man whose name and money his son, Draco, uses to get his way.
Ron's younger sister, and a sweet and shy red-haired girl with an enormous crush on Harry.
Ron's oldest brother still at Hogwarts, a prefect, and a somewhat pompous figure, with, in the end, good intentions.
One of Ron's older brothers, Fred is a beater for the Gryffindor House Quidditch team, and a good solid troublemaker when paired with his twin brother, George. Fred has the slightly louder, more over-the-top sense of humor of the two, but they are identical and usually inseparable. He and his brother George are responsible for passing the Marauder's Map onto Harry.
One of Ron's older brothers, George is a beater for the Gryffindor House Quidditch team, and a good solid troublemaker when paired with his twin brother, Fred. He is somewhat subtler and more tongue-in-cheek than his twin, but otherwise, for the most part identical. Together, the Weasley twins are an infamous, amusing, and charming pair.
Ron's mother; she is very maternal and protective, but also quite strict.
Ron's father, who works in the Misuse of Muggles Artifacts Office within the Ministry of Magic. He loves any sort of Muggle things with a buoyant, childlike enthusiasm. A thoroughly likeable man, Mr. Weasley treats Harry as if he were one of his own (many) children.
Harry's stuffy, overweight, and nasty-tempered Muggle uncle.
Harry's stuffy, underweight, and nasty-tempered Muggle aunt.
Harry's spoiled, overweight, and nasty-tempered Muggle cousin.
Vernon Dursley's visiting sister; a loud, beefy, nasty-tempered Muggle woman who adores attack dogs and enjoys insulting Harry and his late parents.
Harry's mother who sacrificed herself to save Harry from Voldemort; Harry can hear her screams when Dementors are near.
Harry's father, also killed by Voldemort; his animagi stag becomes the shape of Harry's patronus. One of the creators of the Marauder's Map.
The teenaged, pimply, nosy conductor of the Knight Bus.
The driver of the Knight Bus.
The Hogwarts caretaker, who is grouchy and adores nothing but his cat.
Filch's beloved cat.
The rather eccentrically dressed Minister of Magic, very involved in the protection of Harry and Hogwarts against Sirius Black.
The Gryffindor Quidditch captain and keeper.
The handsome Hufflepuff seeker; catches the Snitch when Harry falls from his broom.
The pretty fourth-year Ravenclaw seeker; Harry beats her to the Snitch.
One of Draco Malfoy's unintelligent, lumbering cronies.
The other of Draco Malfoy's unintelligent, lumbering cronies.
A Ravenclaw prefect and Percy's girlfriend.
The barmaid at the Three Broomsticks in Hogsmeade.
A friendly Gryffindor ghost.
A poltergeist who causes lots of harmless trouble at Hogwarts.
One of Hagrid's beloved hippogriffs, Buckbeak attacks Malfoy and is sentenced to death, only to be saved by Harry and Hermione when they turn time back.
Harry's pet owl.
Ron's aging rat; the animal form of Peter Pettigrew.
Hermione's aggressive ginger cat.
Sirius Black's animagi name, when he is a large black dog.
James Potter's animagi name, when he is a stag.
Remus Lupin's werewolf name.
Peter Pettigrew's animagi name, when he is a rat.