Mystique (Secret Agent)
Mystique is known for being evil. How evil? She put together two groups called the Brotherhood of Evil Mutants - that's some serious evil karma there.
So when Mystique got her own comic, was it chock full of her special shape-shifting evil? Not really. The idea was that Professor X rescued Mystique from execution in exchange for being his secret agent who couldn't kill. While she didn't like it, Mystique played along as Xavier's agent, and the comics were full of decent butt-kickery.
As Xavier's secret agent, Mystique wore this black leather outfit, a dramatic change from her usual white outfits.