Type V Anti Heroes

Far from Most Definitely Not a Villain, and range from being simply amoral characters who happen to be pointed at the villains for one reason or another, to being actively malevolent characters, only considered heroes because the villains they fight are much worse.

Sociopathic Heros and many protagonists from Lord Byron fit on this trope, as well as many Nineties Anti-Hero characters, but the tendency was hardly limited to that era, either backwards or forwards.

However, it should be noted that if the conflict is Evil Versus Evil or Black and Grey Morality, the antihero is the lesser of two evils.