This psychopath is one sick puppy! Dr. Gero, the brains behind the Red Ribbon Army, has been Goku's enemy from the latter's childhood. And after Goku obliterated the Red Ribbon Army once and for all, Gero sank into the secret depths of his lair, plotting bitter vengeance. For decades, he sat quietly in the shadows, collecting precious data from all the major conflicts on Earth. His only goal was to destroy Goku, and he designed various versions of androids to carry out the mission.

Despite his insanity, you must admit Gero is a real genius. His androids are diverse in abilities and personalities, creating a broad spectrum of opponents for Goku to defeat. Gero even perfected the art (chilling though it may be) of actually turning a man into a cyborg. He did so with Androids Seventeen and Eighteen, turning twin humans into twin war machines. He even took the ultimate step - turning himself into Android Twenty: immortal, powerful... perfect.

His genius is what killed him in the end. For in his desperation to destroy Goku, he reactivated Seventeen and Eighteen, despite the fact he knew they were as disobedient as teenagers. Teenagers with a very malicious twist. No sooner was Seventeen revived that he recalled his frozen imprisonment. Without hesitation, he cleanly decapitated his creator, smirking wickedly as he smashed the sputtering doctor's impressive brain beneath his feet. While Dragon Ball Z's own Doctor Frankenstein died early in the Cell Saga, his legacy lived much longer, and in the end, his creation Cell did manage to bring about the death of the legendary Son Goku. Of course, we all know death is always temporary for that particular hero...