Sabretooth

Sabretooth, also known as Victor Creed, is a violent brawler who has a deep enmity against Wolverine, but not the psychotic killer of the comics. Little is revealed about Sabretooth except that he had some involvement with Wolverine and Weapon X, and that he is one of Magneto's most loyal followers. Oddly, he was depicted as a loner in the first season, but from the first season's finale (The Cauldron - Part 1) onward he is almost never seen without Magneto.