Android 10000000

Android 10000000 is the final creation of doctor Gero's computer (In dbz SR)and was released right before the z fighters destroyed it. He is a product of a combination of super vegeta's cells and cell's cells ultimately making him enourmously powerful but not enough to defeat a ssj2. However this weakness is overcome when he most of the z fighters and became his perfect form. He absorbed Gohan after the rest of the z fighters and became ulimate perfect form.

Death and Return from hell:Android 10000000 died when facing Maku and Goku. He was sent to hell but absorbed the remenants of Buu to become extremely powerful. He broke out of hell but ended up in a different timeline from the one he was created in. In this timeline Goku was not as powerful as him so he absorbed him,However this backfired and goku gained his powers but his evil personality aswell turn Goku into evil Goku.