Sirius Black

Sirius Black, nicknamed Padfoot, is the last heir of the House of Black, a once notable pure-blood Wizarding family. Sirius's early life proved unhappy; he had come to hate most of his relatives, in particular his mother. He rejected his family's pure-blood elitism and reverence for the Dark Arts. In contrast to his home life, Sirius greatly enjoys life at Hogwarts, where he is inseparable from his best friends: James 'Prongs' Potter, Remus 'Moony' Lupin and Peter 'Wormtail' Pettigrew. Sirius leaves home at the age of sixteen and takes refuge with James and his parents. His outraged mother burns his name off the family tree, but he is left financially independent by his Uncle Alphard's generous bequest. After leaving school, he remained close friends with James and eventually attended James and Lily's wedding as best man. When their son, Harry, is born, the Potters name Sirius as his godfather. When the Potters go into hiding from Voldemort, Sirius suggests they use Pettigrew as Secret-Keeper, believing that Voldemort would hunt him down as the Potter's Secret-Keeper instead of Pettigrew. However, Pettigrew betrays James and Lily, and they are murdered by Voldemort. Sirius tracks Pettigrew down, but during the confrontation Pettigrew fakes his own death and kills twelve Muggles, framing Sirius for betraying the Potters and Pettigrew's and the Muggles' deaths. Sirius is arrested and is imprisoned without trial. Unlike most of the other Azkaban prisoners, Sirius is able to keep his sanity because he knows he is innocent.

Twelve years later, Sirius sees a picture of the Weasley family on the front cover of the Daily Prophet, in which a rat stands perched on Ron's shoulder; the rat is Ron's pet, Scabbers, and Sirius immediately recognises Pettigrew in his Animagus rat form. This knowledge clears his mind and enables him to escape Azkaban, accomplishing this feat by transforming into his Animagus dog form: his severe weight loss from malnutrition and the Dementors' lack of ability to differentiate between unsophisticated canine feelings and insanity allows him to slip through his cell bars. After his escape, Sirius takes refuge in and around Hogsmeade. Knowing that the Dementors are stationed around Hogsmeade and at Hogwarts, Sirius remains in his Animagus form during this time, and is able to enter the Hogwarts grounds without being detected by the Dementors. Towards the end of Prisoner of Azkaban, Harry, Ron, and Hermione confront Sirius and Harry attempts to kill him; however, Lupin, who has learned that Sirius is innocent, prevents Harry from doing this. Scabbers is unmasked as Pettigrew, and Harry begins to view Sirius as a surrogate father, although events swiftly turn against him again – Pettigrew escapes, and Sirius is captured by the Dementors at Hogwarts and sentenced to the "Dementor's Kiss". Harry and Hermione help him escape with Buckbeak, a hippogriff who had also been unjustly condemned.

In Harry Potter and the Goblet of Fire, Sirius has little influence; he mostly gives Harry advice on how to complete the Triwizard Tournament tasks. In Harry Potter and the Order of the Phoenix, Sirius takes refuge in his ancient family home at 12, Grimmauld Place, which he allows to be used as the Order headquarters. His confinement causes depression, and he is frequently withdrawn and antagonistic. When he briefly leaves the house to see Harry off to Hogwarts, his Animagus form is recognised by Draco and Lucius Malfoy, resulting in more threats and warnings. Sirius acts as a brother figure to Harry throughout the book but, according to Rowling, "what Harry craves is a father." Sirius encourages Harry to oppose Dolores Umbridge and her reforms, and strongly approves of Harry starting the secret defensive tutorial group for students, Dumbledore's Army. He also demonstrates a high-level of trust in and respect for Harry, willingly answering the latter's questions about the Order and Voldemort. With his growing power, Voldemort implants a false vision into Harry's mind that Sirius is taken captive and under torture at the Department of Mysteries. Convinced that Voldemort is torturing Sirius, Harry and his friends gain access to the Department of Mysteries. When they are ambushed by Death Eaters, Harry realises that Voldemort has lured him into a trap. Snape, however, alerts the Order that the students have gone to the Ministry after confirming that Sirius is safe at Grimmauld Place. Several Order members arrive at the Ministry, Sirius among them, and battle the Death Eaters. During a frenzied duel with his hated cousin Bellatrix Lestrange, Sirius taunts her for failing to harm him. Bellatrix strikes Sirius with a curse, sending him backwards into a veil in the Death Chamber and thus causing his death.

Sirius makes a final appearance toward the end of Harry Potter and the Deathly Hallows when he is summoned by the Resurrection Stone along with James, Lily, and Remus Lupin to help Harry walk through the Forbidden Forest and sacrifice his life to Voldemort.