Cell

Cell, having found that the Trunks in his timeline had killed 17 and 18, killed him and took the time machine to the main timeline. There he fought the Earth warriors until he was able to absorb 17 and 18, after which he became perfect. In his perfect form, he sucessfully beat most of the Z fighters, only being defeated when Gohan, in a burst of power caused by the pain of losing his father once again, destroyed him once and for all.

Cell is an artificial being, although not an android. He was formed from cells taken from each of the Z warriors by Dr. Gero, which allowed him to take on their strengths and special abilites.