Thanos the greatest enemy of the Avengers was a genocidal warlord from Titan, whose own main objective was to bring stability to the universe by wiping out half of all life at every level, as he believed its massive population would inevitably use up the universe's entire supply of resources and perish.
"I know what it's like to lose. To feel so desperately that you're right, yet to fail nonetheless. It's frightening. Turns the legs to jelly. I ask you, to what end? Dread it. Run from it. Destiny arrives all the same. And now, it's here. Or should I say, I am."