Vilgax (Ben 10)

Ben Tennyson's Arch-Enemy. A sadistic, violent and ambitious alien Evil Overlord, Vilgax is obsessed with getting the Omnitrix so he can use it to create an army of shapeshifting drones able to adapt to any situation, and as such able to defeat anyone in the galaxy. Recognizable by his Cthulhumanoid appearance, he is considered the most dangerous and feared life form in the Ben 10 Universe.