Olormi

Olormi was a very powerful human one million years prior to Dragon Ball Generations, and one of the strongest humans to ever live. He was one of the first two to fuse using the Ultimate Potaras alongside Buubuu, and their fusion formed Bumi.

Background
Olormi trained for a very long while, and eventually became such a significant threat to the universe that the Kaioshin had to fight him. He managed to kill all of them except Buubuu, the Western Supreme Kai, who he was forced to fuse with.