Android 21 is the 21st creation of Dr. Gero. He is the older brother of Androids 17 and 18. He is more powerful than his brother and sister. Like #17 and #18, #21 was turned from a human into an android. 21 escaped when his siblings were captured, because he feared Gero. While he was gone, he trained to be more powerful than Gero, but was captured as soon as he finished training. This android is more powerful than Cell and when Dr. Gero was revived in GT, Gero didn't know that his power was being taken away by 21. 21 is as powerful as Buu.