Sigma

Sigma is the supreme commander of the Mavericks and the main antagonist in the Mega Man X videogame series, serving as the final boss for most games of the series (except for X8 and Command Mission).

Past
Created by Dr. 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. 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). He defects to the Mavericks and assumes the role of their leader. Under Sigma's command, the Mavericks grow into a legion dedicated to the extermination of the human race. Sigma instigates many of the destructive Maverick Wars, with the Maverick Hunters existing to crush Sigma and his minions.

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. 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. 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. It is implied that he grows more insidious and vengeful with each transformation, with each successive plan becoming more and more desperate and aggressive.

Megaman X
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. So with that, Zero and X are forced to fight against the Maverick, with X then reaching Sigma in his palace. Sigma really regrets the X making the choice to stand on the side of humans. He then decides to send his pet theft called Velguarder to face him, then when  Velguarder is destroyed by X.

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.

Megaman X2
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. Cain works on reassembly. 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 disppeared.

Megaman Xtreme
In this game, Sigma uses a Tecno hacker to invade the main computer base Maverick Hunter.

Megaman X3
Whatthe scientist known as Dr. Doppler develops a vaccine to fight the Sigma virus, knowing this Sigma then brainwashes Dr. Doppler, using him to create a new utopian revolt Doppler Town. After X defeats 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. As soon the X appears he mentions that ir was very easy to corrupt Dr. 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. He reaches the corner of X plus Dr. Doppler appears and attacks him with the anti-virus, which causes Sigma to disappear.

Megaman Xtreme 2
Sigma will only appear in Xtreme mode where he reveals that he was responsible for the Erasure incident all the time, although he thabked X for defeating Berkana since she went too far, so they begin to fight, then when Sigma is defeated all souls Reploids return to their bodies.

Megaman X4
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. he promises a plan puts the Maverick Hunter against the Repliforce. 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. hr staged the destruction of Sky Lagoon, he also manages to convince Magma Dragoon  to overthrow the power nucleus of the floating cities while the mechaniloid 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. The General then initiates a war between the Reploids against the Maverick Hunter, also to ensure that your success occurs, it sends Double to spy the X. Soon after the General becomes paranoid and orders him to build a satellite laser, then defeat the General he soon meets with Sigma who tells his plan, and they start another tense fight, even with difficulty X can overcome it, in the end the General appeared and sacrifices himself to can stop it.

Megaman X5
Somehow, Sigma was able to interact with Dr. Wily's conciusness within the virus which revealed the true nature of Zero to Sigma. He awakens the true nature of Zero, Sigma then orders that the known bounty  hunter Dynamo invades the Eurasian space colony and collapses with the Earth. At the beginning of the game, Sigma appears as the first boss and fights against the Maverich Hunter X or Zero, his first form in the two Maverick Hunter appear X or Zero, and then Sigma is defeated the way he wanted what happened  to spread virus everywhere.

The Hunter soon discovers that the space colony Eurasia will collide with the Earth they then just a few minutes and run against the clock, they get the right pieces to feed the Enigma laser, more however laser so delayed the colision, Zero however with the influence of the virus took a bus and destroyed the whole colony collinding with the bus, then Zero is rescued, the Hunters then investigate the Sigma readings, X tries to convince Zero to returns for base plus he refuses then both fight more then the two get exhausted, Sigma takes advantage of the oportunity and tries to attack X, but Zero wake up and retaliates by retreating, X recovers and goes along with Zero to face Sigma, which Sigma reveals plan to fuse Sigma virus with the colony to try emergy the ancient progamation from Zero.

Then when Sigma is destroyed, both Zero and X are damaged, Sigma then appears and attacks X and Zero, but before they die, Zero fires an explosion destroying Sigma immediately.

Megaman X6
In this game, Sigma only appears at the end of the game, then when Gate is defeated he then reveals that he is trying to restore Sigma, but the Sigma code was damaged due to the Eurasia incident. Gate failed to finish his body anyway with his half-unconscious and malfunctioning body, he then carelessly kills the Gate and soon afterwards defies X and Zero for a fight, the Maverick Hunter manages to defeat Sigma at once.

Megaman X7
Some time after the Nightmare incident, X retired from his duties as Maverick Hunter, thereby causing a large increase in Mavericks activities. After the emergence of several illegal groups of Maverick Hunters among them the Red Alert Syndicate led by Red, Sigma then appears and can manipulates Red and his group. He intended to use Axl's DNA one shifter Reploid of the Red Alert to copy the DNA of X and Zero. More however, Axl is suspicious of Red Alert and flees from the place and seek help from Maverick Hunters. Wanting to bring Axl back up he ends up following Sigma's order with no choice.

After the defeat Red and his subordinates, Red sacrifices himself to let Axl go in front. Sigma then confronts the Maverick Hunters X and Zero again, he is defeated promising X and Zero who has returned again, Axl then appears disguised as Red, Sigma tries to own him more Axl returns to his original appearance and shoots Sigma by dropping into a hole.

Megaman X8
Due to the advancement of the technology of the time, Jakob Project was created for the colonization of the Moo, with the creation of the Jakob Orbital Elevator and the New Generation Reploid with which Axl is part, Lumine  the then director of the Jakob Project reveals that all New Generation Reploid it possesses the DNAs of several Reploids, among them Sigma and with such they were immune to the virus and were able to copy the abilities, but later a rebellion begins orchestrated by Vile that not had died in Megaman X3, he kidnaps Lumine and several New Generation Reploids among many others and making them Maverick, and soon after the own Sigma appears and soon reveals it is by behind this everything it from the beginning. When, X, Zero and Axl face Sigma on the Moon, Sigma then reveald that he has manipulated the Jakob Project from the start with the intention of destroying the ancient world and creating a perfect world for him and New Generation Reploid whom he calls children, because since they possess Sigma's own DNA, they could turn into Maverick's will instead of going crazy instead of thinking with him, and how he himself were their equals.

After a long battle with the Sigma, Sigma is finally destroyed, soon after, Lumine appears and reveals how the true mentor behind the whole story, stepping on the dead and fallen body of Sigma and desmonstrating his arrogance about it, he soon states that Sigma fulfilled his purpose and that will not goes back any more.

Maverick Hunter X
In Megaman Hunter X, the reboot of the original game, Sigma is placed as revolting with humans voluntarily due to him who make a Reploid rebellion. After a conversation with Dr. Cain, became obsessed with the Reploids reaching their potentials, and seeing humans as of the Reploids holders. Sigma makes a disaster by hiring criminals to sabotage. Releasing Vile putting both humans and Reploids in danger, creating a large army and exclusive two robberies who believe in their cause, Storm Eagle and Flame Mammoth, Sigma then exhorts himself to destroy that of the man who is the city of Abel.

After of the massacre, Sigma is confronted by Maverick, Sigma is confronted by Maverick Hunters X and Zero, ignored all atempts of X and Zero to talk to stop his plan, they fight, Sigma then coldly says what sacrifices they have made and launches the missiles killing thousand of humans and Reploid, thus Sigma of this fact and announces to end humanity.

Personality
Sigma has moth that differs from the other villains of the X series, while other Reploids lose control their actions and go crazy and turn do not. He studies and learns new things, such as reasoning and the constant preocupation of X and the dark past of Zero, among other things. He is also able to put thee plans on this scale while he is in this state. Despite the majority of infected Mavericks we never saw their real personality because it is masked by the virus. Soon aftet, however, Sigma shown her real personality throughout most of part. He is a great brilliant and destructive strategist who uses it to their advantage.

Sigma is obsessed with destroyng of the humanity, he also keeps control of himself. Sigma has always been insightful, intelligent and imaginative. He also maintains all the weaknesses of his enemies and attacks them as the heart of X and the dark past of Zero and Axl's deportation to the so-called prototype. Sigma's own personality after infection has been very manipulation, sadistic and power-driven. He controlled Dr. Doppler to distribute an anti-virus plus it was actually a virus, he also manipulated General and Colonel a group of Repliforce aimed at praising the Maverick Hunter and causing a war on larges scales, blackmailed a group of mercenaries called of Red Alert, controlled the Red ad its group infected by the virus in the fight against the Maverick Hunter.

Megaman Ruby
Sigma appears in the Mega X episode of the cartoon, although his name is spelled wrong on Light's computer, he sends Vile and Spark Mandrill in time so he could pick up Lightanium's  of Dr. Light, supply so he could finance his war against humans, however, X also travels in time being thwarted by the Mavericks with the help of Megaman as well.

Project X Zone 2
Sigma makes an appearance with one of his boss form as a non-player character.

Marvel vs Capcom: Infinity
Sigma appears in the crossover, he is a major antagonist along with Ultron, and both merge into a new form which is called Ultron Sigma which the main antagonist of the game.

Sonic and Megaman: Worlds Unite
Sigma appears as the main antagonist of Sonic and Megaman comics: World Unite. His real plan was to install the altenative reality mechanism and Unite both so he could rule both worlds.

Trivia

 * Sigma is the eighteeth letter of the Greek alphabet, which fits directry due to its archenemy if called by X, being used as infinite 9t variants thar derives from the letter Phenicia, though the of this letter derives from and his letter Sheen, looks like with W, this is a clear reference to Dr. Wily.