Arawn (LotDs)

"The Emperor of Darkness, King of the Dead, Lord of the Underworld. All these things. He is my species' greatest enemy and greatest fear."

- Frieza on Arawn.

Arawn was originally a powerful Saiyan Warrior that founded the Saiyan Royal bloodline before he gained the power of a Super Saiyan, he became so powerful that eventually he destroyed himself and the home planet of the Saiyan race but even then death was not the end, Arawn became a spirit in the Other World and began to gain power from all that he defeated there until he became a Spectral Entity that could create its own living body and would thereby be hosted in thus allowing him to appear in the Living world.

Trivia

 * In Celtic Myth, Arawn was the God King that ruled the Celtic Overworld, where the dead go when they die.