Walter, the hulking mute monstrosity from the excellent Dark Horse comics series The Mask. Walter was the only character who was strong enough to hurt The Mask; after the third series (The Mask Strikes Back), Walter retired to run for mayor. That series was called Walter: Campaign of Terror and it's every bit as crazy as the original Mask series.
"Try to look at things from my perspective. I was led to believe, that you were under Mr. Cinccinni's employ. So as far as I can see, my only error was doubting your loyalty. THAT and hiring A LOUSY KILLER!" Great job!
Walter isn't able to actually "hurt" a Mask-wearer, but he's proved to be every bit as indestructible as one. If the Mask represents the unstoppable force, then Walter is the immovable object.
In The Mask Strikes Back during the first battle with Walter, the first wearer thinks to himself that Walter is 'killing me'. Walter's hardly indestructible, he's just very, very resilient. Not much of him left after Campaign of Terror.