Dr. Gero (Android 20)

Dr. Gero (ドクター・ゲロ, Dokutā Gero), also known as Android 20 (人造人間20号, Jinzōningen Nijugō), is a brilliant scientist who is the mastermind behind the Red Ribbon Army. After the army's defeat at the hands of Goku, Gero retreated to his mountain laboratory to plot his revenge with his Artificial Humans series. Not until he reached Android 19 did he create an obedient, bloodthirsty servant. Gero then had #19 transplant his brain into an android body, thus turning himself into Android 20 and preventing him from dying of old age. After his second defeat at the hands of the Z Fighters, Gero retreated to his lab to activate Androids 17 and 18, who rebelled, with Android 17 killing the doctor. Though Gero died, he left behind Android 13, Android 14, Android 15, and his ultimate creation, Cell.

Dr. Gero is very cold hearted, willing to stop at nothing to achieve his goals, even kidnapping other people to use in his experiments. He also holds a strong hatred for Goku after Goku had defeated the entire Red Ribbon Army. Dr. Gero's appearance consists of slightly tanned skin, blue eyes, a large bushy white mustache and long hair. He also has a Red Ribbon Army logo located on the hat which hides his visible brain after he turned himself into an android.

Information from:
http://dragonball.wikia.com/