There's a couple of old Psygnosis games that had some really cool "Hero" characters, like the ones in Walker and The Killing Game Show (Fatal Rewind in Europe on the Mega Drive). The Walker would be fairly simple, just a bipedal "chicken walker" type with a machine gun or minigun pod underneath the cockpit, but since the Walker game featured only flat terrain for the Walker to, er, walk on, I can't attest to its "all-terrainability".

The "Hero" character from The Killing Game Show, aside from looking really neat and shiny, especially on the Amiga, had some sort of rapid fire energy weapon, with pick-up options for multi-directional fire. And it could climb up completely vertical walls with ease (which was a major game mechanic).

If all else fails, it might be fun to make some classic Lemmings actors, you know, with that five second countdown and the unforgettable "Oh No! *pop!*".