| Sigma is Mega Man X and Zero's arch nemisis who can never just die. Sigma would go to any lengths to defeat X and Zero. He even went so far as to get Dr. Wily to help him make "the ultimate body".(No, I don't know how he got Dr. Wily to help[maybe there's a hologram of Dr. Wily helping Sigma like there is of Dr. Light helping X]) Sigma was created by Dr. Cain to be the leader of all the maverick hunters. Sigma was the one who defeated Zero when he was a maverick(very close fight, Sigma would have lost to Zero if it wasn't for that migrain Zero had). Also, it was when Sigma turned maverick that X decided to join the maverick hunters. Sigma is the most persistant villian I have ever seen. Every time he is defeated, he makes a new form. In the last six games, Sigma has had over thirteen forms. Sigma finds Zero to be a very unique reploid, so much that he wants Zero to join forces with him( he even created a clone of Zero, which was quickly dispatched by real deal). Sigma is known to work "under cover" and get someone to keep the hunters busy while he does his dirty work. For instance, in X one, he got vile, X2 the X- hunters, X3 Dr. Doppler, X4 General/ Double and so on. The virus that turns reploids maverick is called the Sigma virus, probably because it resembles Sigma's head. Since he can't seem to die, you can expect to see him in the next Mega Man X game.