Obliterator

Obliterator is a Marvel comics supervillain who is a member of the Elders of the Universe - like all members of that society he keeps himself immortal via feeding a single obsession: in his case the obsession of choice is the killing of other life forms, making him a serial mass-murderer.

History
Five billion years ago, the Obliterator discovered that he was immortal and gave a meaning to his life by tracking and killing all of the people of his species but himself; that would keep him busy while he was developing new means of destruction. He was also proud of his goals.

After destroying his species, he decided to search for more living things to kill throughout the universe.

He eventually found the Gardener, who introduced him to others like them, immortal monomaniacs known as the Elders of the Universe. None of them could die because of a special agreement with Death.

However, the Elders prepared a plan to insure absolute immortality, first by waging with Death and later by destroying Galactus. They thought that Galactus' death would cause a new Big Bang and the creation of a new universe where each of the Elders would have Galactus-like powers.

Silver Surfer and Mantis discovered the plan of the Elders, and the Obliterator tried to kill them. Silver Surfer redesigned the Obliterator's equipment to render it harmless, and left him trapped, without weapons, on a world without animal life to kill.

Lacking a purpose in life, the Obliterator was obliterated. He is currently sitting on that world, vainly waiting for something to evolve so that he can kill it.