Crowley

Sold his soul for three extra inches to be added to his penis
Eventually died in a gutter, soul went to Hell tortured until became a demon
Successful crossroads demon, at some point rising to the King of the Crossroads
Initially served with Lilith as her right-hand man, went rogue
Appointed himself the new King of Hell, helping the Winchesters seal Lucifer in his cage
Guided Dean through the process of becoming a demon until Dean was cured
Overthrown & held as a slave when Lucifer escaped from his cage, managed to escape
Joined forces with the Winchesters to seal Lucifer in an alternate reality