Sigma is the name of the primary villian of the Megaman X videogame series. In all of the games in the main series, he has appeared as the primary villian and final boss (with one major exception). Even in off-shoot games of the series (such as Megaman Xtreme) he at least gets a reference at some point in the game.

Sigma is the name of the rebelling reploid first seen in the original Megaman X video game and who is the main villain in subsequent games in the X-series. Sigma rebels against humankind, forming a military force of robots called "Mavericks". His dream is world domination and a lust for power; he is seemingly immortal, as each time X foils his plans and destroys him, Sigma returns. The "Maverick Hunters" is an organization devoted to crushing Sigma and his minions whenever they rear their heads; Megaman X and Zero are among the organization's star members.

Usually Sigma appears as a bulky, bald-headed reploid in most forms. Several of the Megaman X storylines involve Sigma producing a new body to defeat X with at the end of the game.

Story

Sigma is a reploid, and the original leader of the maverick hunters. At the start he was a powerful and righteous leader, even going into battle alone to prevent unnecessary loss of lives for the maverick hunters. This changed on the day that his unit chased down the "red maverick" that had wiped out a whole hunter unit. This maverick turned out to be Zero who was infected by the maverick virus at the time. During their battle, Sigma was mangled by Zero to the point where he was unable to fight back. As Zero was enjoying sigma's suffering, a 'W' suddenly appears on his head causing him immense pain. Sigma seizes the moment to smash zero's forehead for a knockout victory. As Sigma limped out to his unit, he gave them the order to collect Zero's body and take it back to doctor Cain so he could be studied and repaired. At this point, his men ask if he is okay, only to have him brush them aside yelling "Silence!". This is presumably the point where he had become infected by the maverick virus.