he staged the destruction of Sky Lagoon, he also manages to convince Magma Dragoon to overthrow the power nucleus of the floating cities while the mechanaloid Eregon attacks the place, more when both the Reploids and even the Maverick Hunters arrive and see cities fallen on th ground ad soon they blame the Reploids when the Coronel reduses to loose souls, the Reploids are soon labeled Maverick. At fist he tries to convince the Genaral leader of the Repliforce to start a war against the Hunters, but he is fired, so Sigma soon puts his new plan into action. he promises a plan puts the Maverick Hunter against the Repliforce. Some time after his last defeat, Sigma returns he soon became aware of the existence of a new group called Maverick Hunter's Repliforce are created in order to help the hunters against the Maverick, he knowing that they posed a threat. Sigma will only appear in Xtreme mode where he reveals that he was responsible for the Erasure incident all the time, although he thanked X for defeating Berkana since she went too far, so they begin to fight, then when Sigma is defeated all of the reploids souls returned to their bodies. Doppler appears and attacks him with the anti-virus, which causes Sigma to disappear.
Doppler, and that his plan would work out if X had not interfered, so he soon defies X to fight, after a tense fight, X manages to destroy Sigma plus he then back in the form of virus and start chasing the X to own your body. As soon the X appears he mentions that ir was very easy to corrupt Dr. Doppler, he soon regains consciousness ad reveals that he has been controlled by own Sigma thought a brainwasher, but he has also created a new powerful body of battle for Sigma, he then tells X to go after him. Doppler, using him to create a new utopian revolt Doppler Town. Doppler develops a vaccine to fight the Sigma virus, knowing this Sigma then brainwashes Dr. In this game, Sigma uses a Tecno hacker to invade the main computer base Maverick Hunter. While X will face the X-Hunters in their bases, after the X defeats the X-Hunters, he then confronts Sigma, plus Sigma places a fake copy of Zero to face him more the clone is destroyed by Zero with that Sigma escapes more X goes behind him, X then fight against Sigma even with great difficulty he can overcome Sigma and he promises to X that he returned more he does not understand why the X chose is on the side of X as he points out that Zero to the creation of the doctor and he soon disappeared.
Sigma returns and he has his X-Hunters retrieve parts of Zero, so he can reprogram Zero to serve him, plus his plan, however, X can recover the parts of Zero, what Dr. Sigma then faces the X and despite giving work with his first X can overcome him, with that soon after Sigma goes his second form, X has much more difficult to overcome him anyway he can destroy the body of Sigma, soon after Sigma survived and promises to take revenger with a new body. He then decides to send his pet theft called Velguarder to face him, then when Velguarder is destroyed by X. Sigma really regrets the X making the choice to stand on the side of humans. So with that, Zero and X are forced to fight against the Maverick, with X then reaching Sigma in his palace. Sigma then begins his revolt against the humans and the Maverick Hunter himself, he along with other former Maverick Hunter joined him out of loyalty. It is implied that he grows more insidious and vengeful with each transformation, with each successive plan becoming more and more desperate and aggressive.
Although he has been destroyed countless times, Sigma's programming always survives and builds himself a new form, ready to menace the world once again. He often produces a second form after his initial defeat in a game, which frequently has the head (or the crystal on it) as a weak point. Sigma appears as a bulky, bald humanoid in most of his forms his most pronounced feature is a crystal on his forehead, and two parallel scars running through his eyes. Sigma instigates many of the destructive Maverick Wars, with the Maverick Hunters existing to crush Sigma and his minions. Under Sigma's command, the Mavericks grow into a legion dedicated to the extermination of the human race. He defects to the Mavericks and assumes the role of their leader. Although he was once honorable, Sigma unexpectedly goes Maverick in the beginning of Mega Man X and rebelled against humankind (the reason for this was that he was infected by the Maverick Virus, which he received from Zero). Cain, Sigma was considered the finest of the Reploids (having been the first made) and was the first leader of the Maverick Hunters - peace-keeping Reploids who defend humans against their renegade robot counterparts.