Sirius

• Sirius Black was a member of the Black Family. treated horribly by his mother
he joined Gryffindor, breaking the Slytherin history of his family
Sirius became friends with James Potter, Remus Lupin and Peter Pettigrew. they all formed to be the Marauders, a group of students who were up to no good. they made the Marauder's MAP [fallen into Fred and George Weasley which they gave to Harry Potter]. They each became unregistered Animagus to support their werewolf friend, Remus [Moony]. James as a Deer [Prongs], Peter as a rat [Wormtail] and Sirius as a black wolf [Padfoot, Snuffles]

• Soon he became a friend of Lily Evans [Potter]. becoming the godfather of Harry James Potter
Voldemort came after Harry, killing Lily and James. then failing to kill Harry. Sirius tried to make Hagrid give Harry to him as he is Harry;s Godfather, he has full rights to take care of the baby though soon after going after Peter for the murder of his friends

• Upon the way to see Peter. Peter used a spell which killed 12 muggles, then cutting off one of his fingers he fled into the sewer's as a rat. soon after Sirius was sent to Azkaban for 12 years when he escaped to Hogwarts to go after Peter again [which was assumed him going after Harry] and failing then. He was sent to be kissed by a dementor to drain his soul but Harry went back in time [with Hermione] and saved both Buckbeak [a griffin] and Sirius. Both Harry and Sirius would send each other letters of what happens during hogwarts, under the name of snuffles to keep his identity hidden