In all honesty, Thanos almost didn’t even make this list. As I said before, I consider motivation in addition to deeds, and many of Thanos’ actions have been motivated by his love for Lady Death (Death is a sentient being in the Marvel Universe). He has even aided heroes for the general wellbeing of the universe in the past, teaming up with the likes of Adam Warlock, Nova, and the Guardians of the Galaxy. However, one thing that cannot be denied is the body count that Thanos has left in his wake, and that is what landed him on this list. The Mad Titan has killed millions, if not billions, in his existence. He extinguished entire galaxies to show his devotion to Lady Death. He is a walking extinction event. Though there are three more left on this list ranked more evil than he, Thanos has killed more sentient beings than every other character on this list combined. Thanos kills when it suits him, though it is not always his primary goal. However, his power and ambition has put him on the path of slaughter in his every waking moment. Nigh-immortal and constantly yearning for even greater powers, Thanos will likely be the end of the Marvel Universe.