Sigma (シグマ) is a major character and antagonist in the X era, serving as the final boss of most Mega Man X games. He is a highly-advanced Reploid who was built by Dr. Cain to lead the Maverick Hunters, but he developed a hatred for humans and threatened to take over the world. To make matters worse, his mind transformed into the Sigma Virus, a form in which he survived throughout the series even as his bodies were destroyed.
Though Sigma assumes different forms throughout the series, he always retains iconic features such as his bald head, glowing eyes, and a muscular figure with green and/or purple armor.
Sigma debuted in Mega Man X, and his backstory is described in the game's manual. Sigma was created by Dr. Cain to lead the Maverick Hunters, touted as the most powerful and intelligent Reploid of all time. He was given a prestigious SA rank and personally led the 17th Elite Unit.[1] He took his post on March 16th, 20XX, working effectively for at least four months. But on June 4th, 20XX, Sigma suddenly went Maverick himself, having secretly organized an anti-human rebellion using the Maverick Hunters as his army.[note 1] This is the inciting incident of the game, forcing good Hunters such as X and Zero to face him and their former comrades to save humanity.
Sigma is first seen once all eight Mavericks on the Stage Select screen are defeated, when Sigma's portrait appears in the center of the screen. X does not face Sigma until Sigma Stage 4, the final stage. After X climbs a tower, Sigma teleports in and gloats that he could destroy X, but will leave him to his pet, Velguarder. Once X defeats it, Sigma returns and applauds his strength before discarding his cloak to face him with a beam saber. Once Sigma is defeated in this form, his body is destroyed and only his head remains, which ascends into a giant wolf-like robot in the background: Wolf Sigma (ウルフシグマ). Once X is victorious, the robot begins to explode and Sigma cries out, asking X why he fights against his fellow Reploids. X flees, leaving Sigma to perish.
After the credits roll, Sigma's face reappears on a monitor, revealing that X only succeeded in destroying his body and that his "spirit" remains intact. He threatens to return in other bodies to continue his plans.
Mega Man X2
In Mega Man X2, Sigma returns thanks to his underlings, the X-Hunters. Although Sigma was destroyed, his rebellion survived and went into hiding, until the X-Hunters started their plan to resurrect Zero as a Maverick and crush the Maverick Hunters.
Mega Man Xtreme
In Mega Man Xtreme, Sigma returns under unexplained circumstances.
Mega Man X3
In Mega Man X3, Sigma returns when Dr. Doppler becomes infected by the Sigma Virus, bringing him under his control.
Mega Man Xtreme 2
In Mega Man Xtreme 2, Sigma returns under unexplained circumstances, only appearing in Extreme Mode.
Mega Man X4
In Mega Man X4, Sigma returns under unexplained circumstances. He works from the shadows, meeting with General of Repliforce and urging him to confront the Maverick Hunters about their willingness to destroy Reploids to satisfy the humans.
When Zero faces Sigma, a flashback shows the two's first encounter. Back when he led the Maverick Hunters, Sigma went alone to stop Zero's rampage after he was first awakened. He was overpowered by Zero in their battle, until Zero was suddenly immobilized by the Maverick Virus taking hold.[2] Sigma took the chance to knock him unconscious, ordering the Hunters to collect him for study. However, Sigma had secretly been exposed to the Maverick Virus as well, and over time it began influencing his thoughts towards rebellion against the humans.
Mega Man X5
In Mega Man X5, Sigma returns under unexplained circumstances. After meeting an old man (Dr. Wily) via the Sigma Virus, Sigma learns of Zero's original nature and how to awaken him to it once more. He hires Dynamo and initiates a plan to make Zero into Awakened Zero so he will fight X.
Mega Man X6
In Mega Man X6, Sigma is resurrected by Gate as a last resort should his plans fail. However, his work is incomplete, leaving Sigma as a raving lunatic who stutters and slurs his words.
Mega Man X7
In Mega Man X7, Sigma returns under unexplained circumstances, more lucid than his previous appearance. Going by the moniker of the Professor (センセイ, lit. "Teacher"), Sigma contacts Red as part of a new plan to obtain X and Zero's DNA.
Sigma appears as an unlockable Hunter Program in the crossover mobile game Mega Man X DiVE. He is an S-rank Program and was added to the game on 2 July 2020. His Active Skills are Head Beams and Dash Blade, which are references to attacks he used as a boss in Mega Man X. Sigma also had several variants released as Hunter Programs:
In the Zero era, Sigma is briefly mentioned in Mega Man Zero 2, as records state that the Mother Elf was used to finally neutralize the Sigma Virus and end the Maverick Wars. This game was released before Sigma's final death was established in Mega Man X8, but it's still possible that the Sigma Virus had lingered on without him until this point in history.
Other Game Appearances
Other Media
Behind the Scenes
Creation
Concept art for the villains of Mega Man X, from Mega Man X Official Complete Works.
Keiji Inafune originally designed three separate characters — a tall one, a short one, and a fat one — to act as a triumvirate of villains for Mega Man X. However, they were eventually merged into a single character, Sigma (the idea of three villains was later reused for the X-Hunters in Mega Man X2). His mark was originally a cobra with a "W" shape in its hood to foreshadow Sigma's connection to Dr. Wily, though it was eventually changed to a wolf with a "Σ" shape in its jaws instead. The uppercase sigma was intentionally chosen for its resemblance to a W rotated ninety degrees.
Nomenclature
Language
Name
Origin
Japanese
Sigma (シグマ)
Named after the Greek letter sigma (uppercase Σ, lowercase σ), which is used as the mathematical notation for summation. This may refer to Sigma's reputation as the most powerful Reploid of all time, the sum of all Reploid technology. An uppercase sigma (Σ) is also used as the symbol for Mavericks throughout the X era.
English
Notes
↑The dates after November 22nd differ in the Japanese version of "The Journal of Dr. Cain", being on average a month or two later than the dates in the English version. Additionally, it says Sigma led the Hunters for two years, while the English version only indicates four months.
