Slipknot is an interesting band. Since 1997, each member of the band has had a unique mask. The mask belongs to Jim Root, one of the two guitarists.
This is not an original mask by Jim Root. Originally, like all new Slipknot members, Jim Root did not choose a mask and instead was given the black bondage mask of the member he replaced, Josh Brainard. But the inherited mask was just too difficult to play, and Root wanted a mask of his own, so he chose the one he wanted.
