Wolverine's arch-enemy, another former member of Weapon X, Victor Creed and I were never really friends or enemies, but when Weapon X was reformed as a covert strike team, they sold me on
rejoining by having Sabretooth cut off one of my arms with his new claws then injecting me with something that amped up my healing factor to regrow the lost arm at a rate that puts The Lizard to shame, and for once scar free.... So yeah I joined. Sabretooth also killed my girlfriend Copycat.
The whole Weapon X 2 thing was short lived though, Tooth and I have the occasional run-ins since that.
The biggest run-in recently where I hunt down the bastard because I think he killed my parents. He didn't. It was actually me, and he just watched. But my memory is all kinds of screwed-up.