Sirius Black came from a long line of Pureblooded wizards, most of whom seemed to have been Slytherins. His mother and father were of the thinking that to be a Black made you almost royal, and they looked down upon halfbloods and Mudbloods with disdain. They were early supporters of Voldemort before his bid for power became too ruthless, and Sirius's younger brother Regulus Black was even a Death Eater before he was killed for attempting to defect.

His family did not think much of Sirius, calling him a traitor to the bloodline and an abomination, and they translated this same disapproval to other members of the family who did not uphold the Black family values. Sirius's lineage is intricate and extended, and includes the following people:

- Phineas Nigellus - former Headmaster of Hogwarts - great-great grandfather

- Araminta Meliflua - tried to force a law to legalise Muggle-hunting - cousin

- Elladora - beheaded aged house-elves - aunt

- Nymphadora Tonks - Auror and Morphamagus - second cousin

- Andromeda - Tonks's mother - cousin (married Muggleborn named Ted Tonks)

- Narcissa Black Malfoy - Draco's mother, Lucius's wife - cousin

- Bellatrix Lestrange - Death Eater - cousin (married to Rodolphus Lestrange)

Sirius was also related by marriage and by blood to the Weasleys. His family home was also under the 'care' of an aged and insane house-elf nakmed Kreacher, who Sirius never really liked very much and treated badly.

When Sirius was sixteen years old he ran away from home, preferring to kip out at the Potters' until he was seventeen and able to get a place of his own - thanks to an inheritance of gold from Uncle Alphard.

Sirius was James Potter’s best friend at Hogwarts. They were like brothers, particularly after the Potters all but adopted a teenage Sirius as a second son. Both were exceptionally-bright and troublemakers (often hanging out in the Three Broomsticks making Rosmerta laugh, when not in detention. They were extremely cruel to fellow student Severus "Snivellus" Snape - James in particular. Young Sirius was extremely handsome and somewhat haughty, brilliant and unaware of the appreciative gazes from his female classmates. When bored, Sirius was easily tempted by tormenting others - especially if it were James doing the tormenting. He was also one of if not the only person James would listen to.

Sirius was named James’s best man at his wedding and is Godfather to Harry. When James and Lily went into hiding from Voldemort, Sirius was set to be their Secret-Keeper; their whereabouts would be hidden inside him using a Fidelius Charm, and Voldemort would never find the Potters so long as Sirius never told anyone where they were. He was set to go into hiding as well, when at the last minute he switched with Peter Pettigrew thinking he would outwit Voldemort by using the last person anyone would expect.

Sirius had a flying motorbike that he rode around upon and loved. He was the second to arrive on the scene at Godric’s Hollow the night of James and Lily’s deaths, after Hagrid, to whom he gave his bike and said, “I won’t be needing it anymore." Sirius had realised that Peter had betrayed the Potters and set out to find him. Upon being cornered Peter framed Sirius and faked his own death, leaving Sirius to be taken away by twenty members of the Magical Law Enforcement Squad and sentenced to Azkaban without a trial (as ordered by Barty Crouch Sr.). He spent 12 years in Azkaban, and the only thing that kept him from losing his mind was knowing that he was innocent. He kept his powers and was able to turn into his Animagus form to stave off the insanity.

Upon seeing a picture of Ron’s rat Scabbers in the Prophet (given to him by Fudge during a Ministry inspection of Azkaban), Sirius became obsessed with escape and finally managed it in 1993, when he set out to find Scabbers - who was really Peter - and commit the murder he did the time for. After a confrontation in the Shack during Harry's third year, the truth was revealed: Sirius is innocent. However Peter's escape forced Sirius to go into hiding, where he remained until Harry's fourth year when he turned up again to help Harry through the Tri-Wizard Tournament and then later to "alert the old crowd" of Voldemort's return, per Dumbledore's request. When last we heard of Sirius, he was told to "lie low at Lupin's for a while," but after the events of Harry's fourth year it became clear that Sirius had spent the majority of the summer hiding out in his old family home.

In 1996, during an attempt by Voldemort to obtain a particular item from the Department of Mysteries within the Ministry of Magic, Sirius Black was hit in the chest by a Stupification Spell cast by Bellatrix Lestrange and knocked into a strange device resembling an ancient stone archway draped in a tattered veil, from which can be heard (by certain people who are also able to see thestrals, the strange horse-like creatures one can only view if one has witnessed death) softly whispering voices. He vanished, and is presumed dead.

- Sirius's motorbike is - according to the film - an early 1970s Triumph, and at least a 650. Triumphs are British-made, and fairly pricey.

- The Black family mansion - a vast, ancient house full of cranky portraits and expensive bric-a-brac - was located at number twelve, Grimmauld Place. It is Unplottable, meaning it cannot be mapped or seen by Muggles or anyone not meant to see it.

- At the time of OotP, Sirius was still on the run from the law with a ten thousand Galleon reward on his head.

- Sirius's Gringotts vault number is 711.

- He used to like doing the Prophet crossword.

- During separate detentions, James and Sirius would speak to each other using a small, portable two-way mirror.