Yes, Mankind's iconic mask was first designed for The Undertaker. Kind of ironic considering that when Mankind debuted, he ended up feuding with Undertaker extensively. The decision not to feature such a mask on Taker, was likely down to how uncomfortable the design was. Foley would often complain that it wasn't a great fit, and Taker would have had the sway to shoot such a thing down. That's likely what happened with several designs on this list, The Undertaker probably said "no" to a few of them. He's always had a great instinct for what is right in terms of business. Together with the WWF creative team, Mark Calaway's work has allowed the greatest character in wrestling history to reign for twenty five years now.
