When the Potters became aware that Harry was Voldemort's specific target, Albus Dumbledore advised them to go into hiding using the Fidelius Charm, a highly complex spell allowing a secret to be concealed within another person.

Sirius, however, worried that Voldemort would immediately suspect him of being the Potters' Secret Keeper and would target him; so he convinced the Potters to reassign Pettigrew as their Secret Keeper because he did not believe Voldemort would ever suspect a "weak, talentless thing" like Pettigrew.

However, Pettigrew outwitted him: confronted by Sirius on a city street, he created an explosion, faking his own death (leaving a severed finger behind as evidence) and killing twelve Muggles in the process.

Sirius was arrested, accused of murdering Pettigrew and the muggles and of serving Voldemort, and was promptly thrown in prison by Barty Crouch, Sr. without receiving a trial.

Sirius states that unlike most other Azkaban prisoners (who often became insane during their terms of imprisonment), he was able to keep his sanity because he knew he was innocent, and also used his Animagus form to ward off the Dementors, who are unable to perceive unsophisticated canine minds.

Twelve years into his sentence, Sirius sees a picture of the Weasley family on the front cover of the Daily Prophet.

This serves as a turning point in the series and sets the events of the third novel, as Sirius immediately recognises Scabbers as Pettigrew's Animagus form.

He is the first person known to have escaped the wizard prison by his own means, accomplishing this feat by transforming into his Animagus dog form.

The dementors' inability to detect Animagi, along with his severe weight loss from malnutrition, allow him to slip through his cell bars.

After his escape, Sirius takes refuge in and around Hogsmeade, intent on exacting revenge upon Pettigrew and remaining near Harry.

Sirius, worried, returns to Britain when Harry tells him that his scar has begun hurting him again (a signal of Voldemort's presence), and when there are reports of Death Eater activities at the Quidditch World Cup.

His confinement causes depression, and he is frequently withdrawn and antagonistic – especially so by Snape's increasingly important role within the Order.

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.

Harry and Sirius stay in touch through owls and the Floo Network, a system to communicate through fireplaces.

Sirius is nearly captured by Dolores Umbridge, a Ministry official who is monitoring the Network and the owl mail in and out of Hogwarts.

Near the middle of the novel, a large number of Death Eaters, including Sirius's cousin Bellatrix, escape Azkaban.

Voldemort plants a false vision in Harry's mind that shows Sirius being tortured at the Department of Mysteries.

The Order immediately sends a rescue team including Remus Lupin, Nymphadora Tonks, Alastor Moody, and Kingsley Shacklebolt.

Harry inherits all of Sirius's possessions, including the house at Grimmauld Place, the house-elf Kreacher, and Buckbeak the Hippogriff.

Appearing as a ghostly figure alongside Lily, James and Lupin, Sirius supports Harry's walk into death and assures him that dying is, "Quicker and easier than falling asleep."

Oldman revealed that he accepted the part because he needed the money, as he had not taken on any major work in several years in order to spend more time with his family.

[citation needed] Just as in the book, Sirius returns via the Resurrection Stone in The Deathly Hallows – Part 2 alongside James, Lily and Remus right before Harry enters the Forbidden Forest to face Voldemort.

The character is referenced for the final time in the last scene, where it is revealed that Harry and Ginny's first born son was named after both James and Sirius.

[14] As a student at Hogwarts, Sirius was well-known for being a troublemaker, and once mentioned to Harry that he, James, Lupin, and Pettigrew "were all idiots".

"[21] Unlike his parents and brother, Sirius detested the Dark Arts and did not believe in the so-called purity of blood.

However, in the following fight against his cousin Bellatrix, he underestimated his opponent and even openly mocked her, before being hit by an unknown spell that blew Sirius backwards and he disappeared through the veil in the Death Chamber.

However, they asserted what most appeals to them about the character is the father-son relationship that begins to form between him and Harry before Sirius's death.

[24] In January 2006, Rowling donated a hand-drawn version of the Black family tree to a Book Aid International charity auction.

The tree was purchased for £30,000 on behalf of the British actor Daniel Radcliffe, who plays Harry Potter in the film series.