Sirius Black
Sirius was an animagus and was able to transform into a big black dog, (a Grim) which is an omen of death, at will. He, along with James Potter and Peter Pettigrew became Animagus to help Remus Lupin with his transformations. He was the first wizard to escape Azkaban prison, after being kept there twelve years for a crime that he did not commit. The betrayal of James and Lily Potter, the murder of Peter Pettigrew and 12 muggles with an unknown curse. Harry found out, after a year of believing otherwise, that Sirius was an innocent man, and helped him evade capture from the Ministry of Magic. Sirius went on the run before returning to his (empty) childhood home, 12 Grimmauld Place, and offered it up as headquarters for the Order of the Phoenix upon Voldemort's return. He was killed in a battle at the Ministry of Magic by his cousin, a Death Eater, Bellatrix Lestrange in Harry's (his Godson's)5th year at Hogwarts. He returned during Harry's 7th year along with James, Lily and Remus, after being resurrected with the help of the Resurrection stone in a hazy form.