Attened Hogwarts for 7 years, was part of the infamous group of pranksters' known as the 'Marauders', Remus Lupin(Moony), Peter Pettigrew (wormtail), himself, and James Potter (Prongs). He was framed by Peter Pettigrew after the deaths of Lily and James Potter, and sent to Azkaban prision for 12 years before he escaped! Something one had ever done before.
Sirius is also an animagi, he transforms into a large, black, bear-like dog. Known as Padfoot, and/or Snuffles.
He was a fan-damn-tastic (straight) hottie.
Dumbledore: "Sirius was a brave, clever, and energetic man, and such men are not usually content to sit at home in hiding while they believe others to be in danger."
Harry Potter's presumed dead God-father/doggy. One time best friend of James Potter and Remus Lupin, "killed" at the hands of one evil bitch of a cousin Bellatrix Lestrange. Also, hands off, as he is betrothed to the aforementioned Remus Lupin.
The Sexy Marauder
Sirius - "You can't be serious, I'm Sirius!"
James - "Sirius, seriously, that joke is really old."
Sirius - "Seriously?"
For the next two years, Sirius remained in hiding. He served as a confidant to his godson, Harry Potter, through letters and secret meetings. In Harry's fifth year, however, Sirius went to save Harry in a battle against Voldemort and some of his Death Eaters. Bellatrix Lestrange, a cousin of Sirius's as well as a Death Eater, sent a spell towards Sirius. As a result, he fell beyond a dark veil, where he is presumed to be dead.
"I trusted you," he stuttered.
The man laughed bitterly. "You were always dim-witted, Sirius."