<P> After Harry, Ron and Hermione witness Buckbeak's execution, Ron's pet rat Scabbers bites him and escapes . When Ron gives chase, a large dog appears and drags both Ron and Scabbers into a hole at the Whomping Willow's base, which leads to an underground passage to the Shrieking Shack . The trio discover that the dog is actually Sirius, who is an Animagus . Lupin arrives and embraces Sirius as an old friend . He admits to being a werewolf, and explains that Sirius is innocent . Sirius was falsely accused of betraying the Potters to Voldemort, and murdering twelve Muggles and their mutual friend, Peter Pettigrew . It is revealed that Scabbers is actually Pettigrew, an Animagus who committed the crime for which Sirius was convicted, and had betrayed the Potters . After forcing him back into a human, Lupin and Sirius prepare to kill him, but Harry convinces them to turn Pettigrew over to the dementors . </P> <P> As the group departs, the full moon rises; Lupin transforms into a werewolf, and Sirius transforms into his dog form to fight him off . In the chaos, Pettigrew transforms back into a rat and escapes . Sirius and Harry are attacked by dementors and Harry sees a figure in the distance save them by casting a powerful Patronus spell . He believes the mysterious figure is his deceased father, and passes out . He awakens to discover that Sirius has been captured and sentenced to the Dementor's Kiss . Acting on Dumbledore's advice, Harry and Hermione travel back in time with Hermione's Time Turner, and watch themselves and Ron repeat the night's events . They save Buckbeak from execution and witness the Dementors overpower Sirius and Harry . The present Harry realises that it was actually he who conjured the Patronus, and does so again . Harry and Hermione rescue Sirius, who escapes with Buckbeak . Lupin resigns to prevent an uproar from parents over a werewolf teaching their children . Sirius sends Harry a Firebolt broom, and Harry happily takes it for a ride . </P> <Ul> <Li> Daniel Radcliffe as Harry Potter, a 13 - year - old British wizard famous for surviving his parents' murder at the hands of the evil dark wizard Lord Voldemort as an infant, who now enters his third year at Hogwarts School of Witchcraft and Wizardry . </Li> <Li> Rupert Grint as Ron Weasley, Harry's best friend at Hogwarts . </Li> <Li> Emma Watson as Hermione Granger, Harry's Muggle - born best friend and the trio's brains . </Li> <Li> Robbie Coltrane as Rubeus Hagrid, the gamekeeper and new Care of Magical Creatures teacher at Hogwarts . </Li> <Li> Michael Gambon as Albus Dumbledore, the headmaster of Hogwarts and one of the greatest wizards of the age . Gambon assumed the role after Richard Harris, who played Dumbledore in the previous two films, died on 25 October 2002 . Despite his illness, Harris was determined to film his part, telling a visiting David Heyman not to recast the role . Four months after Harris's death, Cuarón chose Gambon as his replacement . Gambon was unconcerned with bettering or copying Harris, instead giving his own interpretation, putting on a slight Irish accent for the role, as well as completing his scenes in three weeks . Rumours of Ian McKellen being offered the role started to spread, but when asked he rejected the rumours and stated he had played a similar character in Gandalf of The Lord of the Rings trilogy . He also stated it would have been inappropriate to take Harris' role, as the late actor had called McKellen a "dreadful" actor . Harris's family had expressed an interest in seeing Harris's close friend Peter O'Toole being chosen as his replacement . </Li> <Li> Richard Griffiths as Vernon Dursley, Harry's Muggle uncle . </Li> <Li> Gary Oldman as Sirius Black, Harry's infamous godfather, who escapes from the Wizarding prison Azkaban after serving twelve years there for being falsely accused of being the Death Eater who betrayed Harry's parents to Voldemort . Oldman accepted the part because he needed the money, as he had not taken on any major work in several years after deciding to spend more time with his children . He drew inspiration from Cuarón, whom he described as having "such enthusiasm and a joy for life," and compared Sirius to John Lennon . He was "surprised by how difficult it was to pull off", comparing the role to Shakespearean dialogue . Oldman suggested Sirius's hairstyle, while Cuarón designed his tattoos . He had read the first book, and his children were fans of the series . The part made Oldman a hero with his children and their schoolmates . </Li> <Li> Alan Rickman as Severus Snape, the Potions teacher at Hogwarts and head of Slytherin . </Li> <Li> Fiona Shaw as Petunia Dursley, Harry's Muggle aunt . </Li> <Li> Maggie Smith as Minerva McGonagall, Deputy Headmistress of Hogwarts, the Transfiguration teacher at Hogwarts and head of Gryffindor . </Li> <Li> Tom Felton as Draco Malfoy, Harry's arch rival and a Slytherin house student </Li> <Li> Timothy Spall as Peter Pettigrew, a friend of Harry's parents said to have been killed by Sirius Black, but was later revealed to have been the real Death Eater who betrayed Harry's parents to Voldemort . </Li> <Li> David Thewlis as Remus Lupin, the new Defence Against the Dark Arts teacher at Hogwarts and a werewolf . Thewlis, who had previously auditioned for the role of Quirinus Quirrell in Harry Potter and the Philosopher's Stone, was Cuarón's first choice for the role of Professor Lupin . He accepted the role on advice from Ian Hart, who was cast as Quirrell, and had told him that Professor Lupin was "the best part in the book ." Cuarón told Thewlis that he thought Lupin was gay, describing him as a "gay junkie", although his idea turned out to be incorrect . Thewlis had seen the first two films and had only read part of the first book, although after taking the role he read the third . He was excited about the prospect of making a children's film, and enjoyed its filming . </Li> <Li> Emma Thompson as Sybill Trelawney, the Divination teacher at Hogwarts . </Li> </Ul> <Li> Daniel Radcliffe as Harry Potter, a 13 - year - old British wizard famous for surviving his parents' murder at the hands of the evil dark wizard Lord Voldemort as an infant, who now enters his third year at Hogwarts School of Witchcraft and Wizardry . </Li>

Main characters in harry potter prisoner of azkaban
find me the text answering this question