Dr. Gero's master creation, in a nutschell. Cell is abeing, created out of cell's from the greatest fighters in the universe. Goku, Krillin, Piccolo, freeza, you name it, he's got it. At first, the project takes too long for Dr. Gero to finish it, but as his laboratory is destroyed by Krillin and Trunks, Cell keeps growing in a safe place under the lab. He is teh 21st Android. In the future he kills Trunks to use his timemachine to get back to the time where Android 17 and 18 haven't wrecked the world yet. If he wouldn't have done this, he'd never become perfect. After quite a while he get's killed by Gohan, as he reches the next Saiyan level.