Peter Pettigrew, the Secret Keeper for the Potter family who betrayed them to Voldemort. Sirius Black was originally meant to be the secret keeper for James and Lily Potter, but Sirius thought Voldemort was on to him (he thought that Remus Lupin was a spy), therefore passing on the Secret Keeper to Peter Pettigrew.
Sirius Black was believed to be the Potters' Secret Keeper, but he secretly switched with Peter Pettigrew, who turned out to be a mole. James' bullying behavior at Hogwarts and his relationship with Peter contributed to the tragic events that led to the Potters' deaths and the rise of Harry Potter's story.
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. He spent the next twelve years in Azkaban, brooding over his friends' deaths and obsessing over Pettigrew's betrayal.
Sirius Black is introduced in the third Harry Potter installment as the Prisoner of Azkaban, a dark and menacing figure feared by the Wizarding World almost as much as Voldemort himself. Everyone believes he's a mass murderer who betrayed Harry Potter's parents to the Dark Side.
Why didn't Harry go live with Sirius after his parents died?
Lily's blood and protection lived on and would last until he came of age. Therefore, if Harry had gone to live with Sirius while he was still underage, he would not be safe from Voldemort.
His help at the Ministry of Magic might result in a smoother mission. Thanks for A2A. No. Sirius had no idea that Harry was a Horcrux, and I think that is one of the kindest things that was done.
Dumbledore's lack of belief that Sirius is innocent is also suspect. Sirius was a member of the Order of the Phoenix which fought against Death Eaters, but Sirius also was as close to James as a brother, the Potters even took him in when he ran away from home.
Until the climax of Prisoner of Azkaban, Lupin believed Sirius Black was guilty of murdering 12 Muggles, betraying Lily and James Potter, and killing Peter Pettigrew. He eventually discovered the truth — that Sirius was innocent, and the very much alive Peter was the traitor.
Sirius also disliked Regulus because of his ambition to become a Death Eater, but he was unaware that Regulus later attempted to destroy one of Voldemort's Horcruxes. Sirius regretted how young his brother died and wished Regulus hadn't been as soft to go with what their parents told him to do.
Regulus never told Kreacher that he had turned away from Voldemort since he knew it would be safer for his family if they continued with the pure-blood ideology. So, Mrs. Black and Sirius never learned the truth—and Kreacher dutifully kept his secret until Harry Potter showed kindness and offered help.
Remus fought at the Battle of Hogwarts on 2 May 1998, during which his wife was murdered by Bellatrix Lestrange. Remus was also murdered by Death Eater Antonin Dolohov, during the first half of the same battle. His death was possibly avenged by Filius Flitwick.
Sirius treated him like this because he hated his family and their house. Kreacher resented Sirius because of this treatment, and he later betrayed Sirius by telling Bellatrix about how she could exploit his close relationship with Harry, eventually resulting in Sirius' death.
Sirius's intense love for James, his grief after James's death, and his anger towards Peter drove him to insanity, getting him locked up in Azkaban for crimes he never committed.
In fact, James outright tells Lily that he's bullying Severus Snape because of the “fact that he exists, if you know what I mean”. James Potter saved Severus Snape from the werewolf prank before the Snape's Worst Memory scene happened. The mastermind of said prank is Sirius Black, James' best friend.
In the film, Bellatrix hit Sirius with the Killing Curse, Avada Kedavra, killing him before he passes through the Veil. In the book, the curse that hits Sirius is not identified (although it is rumoured to be Stupefy because of the red light), and him being knocked through the Veil is what causes his death.
The Malfoys are related to the Black family through Narcissa (a first cousin of Sirius Black, Harry's godfather), which makes Draco a nephew of both Bellatrix Lestrange and Andromeda Tonks.
Family. Snape's family background is mostly shown in flashbacks during the course of the last three novels. Snape was born to Eileen Prince, a witch, and Tobias Snape, a Muggle, making him a half-blood (hence the name, "Half-Blood Prince").
Although Sirius was the older son and heir, Regulus's parents liked him more, as he upheld the Black family traditions and was loyal to his parents, although his brother Sirius didn't follow any of the traditions. Regulus is two years younger than Sirius.
And Remus was in love with Sirius (also hopelessly, because Sirius only had eyes for James). Then James was killed, Sirius was imprisoned, Remus was outcasted, and Peter was ratatouilled.
Sirius Black proved he did not care about Remus. So of course, he would suspect him to be the traitor. Now, why would Remus Lupin suspect Sirius Black to be the traitor? Because he had already betrayed him once before.
Although the slimy character was close friends with James during their time together at Hogwarts, Pettigrew ultimately abandoned his friends to join the dark side. In order to prove his loyalty to Voldemort, Pettigrew was obligated to hand over the Potters' hiding location, otherwise he would be killed.
Following Voldemort's fall, Snape made no attempt to find his master, for he, like other Death Eaters, believed that Voldemort was dead, and he could use Dumbledore's protection to avoid being sent to Azkaban.
With effort, Snape was able to prevent Albus Dumbledore from learning the truth about his loyalties. Due to Snape's facade, Albus Dumbledore trusted Snape for reasons that were kept between them both until Snape murdered him.
