Slipknot is an interesting band. Since 1997, each member of the band has had a unique mask. The mask belongs to the band's guitarist Mick Thomson.
Thomson's masks have all been based on his original hockey mask idea, albeit with some major tweaks to incorporate his own style. The guitarist's masks have evolved, but for over a decade, the changes have been minor, so his signature look has remained relatively the same during the last few album cycles. The metallic grill over the mouth is something he has stuck with and made his own, yet it is also the way his newer masks are linked to the original.
As one of the band members who has modified his mask the least, Thomson summed up his feelings on the matter when he said, "If you know who you are, you don't need change. I think I pretty much nailed it with this one for being able to get across how I am," when discussing the mask of the "Vol 3: The Subliminal Verses" era in 2004.