He may not be Superman's most cunning or intelligent foe, but Doomsday is still the only one of them to have actually killed the Man of Steel. A genetically engineered Kryptonian weapon, his battle with Superman took place through the whole of Metropolis, and only ended when the monster quite literally beat the hero to death in front of his friends and loved ones. Sure, Superman returned, but this was still an historic moment. It's a shame then that subsequent appearances have somewhat watered down this iconic villain, but at the time, The Death of Superman was a real game changing moment in the comic book industry. Seeing a beaten and bloodied Superman laying dead with his cape billowing in the wind was something fans never expected, and for that alone, Doomsday deserves to take such a high position as one of the hero's biggest threats.
