Dr. Thomas Light created a robot he named “Mega Man X” which was the first of its kind to be able to think and make its own decisions. Fearing that this new robot could be dangerous, but lacking the time to find out for sure himself, Dr. Light sealed X in a capsule to be opened in the future, when the robot’s loyalty could be determined.
A man by the name of Dr. Cain found X’s capsule and released the robot despite the warnings Dr. Light had posted on the capsule. This new scientist was immediately impressed by X’s advanced, humanlike intelligence, and using X as a model—though there were things he had to change since he either didn’t understand how they worked, or he wasn’t able to duplicate them—Cain created more robots similar to X which he hence called “Reploids.” Unfortunately for Dr. Cain, Dr. Light’s greatest fear came true. The new robots rebelled against humankind and became a powerful enemy called the Mavericks.
True and loyal, X took it upon himself to stop the Mavericks, which were led by Sigma, one of Dr. Cain’s Reploids. X wasn’t alone, however; he was almost immediately aided by the mysterious Zero. He also encountered capsules left by the late Dr. Light, which possessed holographic messages from the scientist, and useful power-up items. Using these power-ups, X increased his meager abilities and brought himself back on par with his enemies—and beyond.
During a climatic fight with Vile, Zero destroyed himself to save X, allowing X to slay Vile. Alone now, X went on to defeat Sigma and bring the Maverick uprising to a halt.
This is the tale of Mega Man X1.
Eventually more Reploids went Maverick, spawning a group of sane robots to form the Maverick Hunters. Led by X, they struggled to fight off the forces that were trying to eliminate all of mankind. During this, X discovered that Zero’s parts were in the hands of three X-Hunters, Agile, Violen, and Serges. X also discovered exactly into who’s hands Zero was to be delivered—namely, Sigma.
Despite the odds, Zero was rebuilt, no worse for wear, and the Maverick Hunters put Sigma out of commission.
For a time.
This is where the tale of Mega Man X2 ends and the story of Mega Man X3 picks up. Dr. Doppler, a Reploid scientist, is possessed by a virus that is none other than Sigma himself, reduced to portable computer code. Sigma finds bounty in this form, however, since it allows him to inhibit whatever robot body he wants. He gets Doppler to construct for him a giant, invincible body, but almost before he can get inside it, X shows up at his front door to take him down.
Sigma’s third fall to a special anti-virus developed by Doppler is no more guaranteed to be his last than any of his others. In fact, he pops up perfectly healthy in Mega Man X4 to start a war between the Maverick Hunters and the elite fighting team known as the Repliforce. And again in Mega Man X5 to cause a cataclysm related to the space colony Eurasia which crashes into the Earth, and the Nightmare Phenomena in Mega Man X6 which plagued Reploids and created some unusual circumstances. Sigma was also behind the attacks by a Reploid group called Red Alert in Mega Man X7, where Axl’s shape-changing abilities were the prize to a bizarre game. In fact, Sigma even had his gloves in the events of Mega Man X8, although he can’t be blamed completely for that (or can he?). It is yet to be seen what, if anything, will be required to finish Sigma off for good.
On the other hand, the Maverick Hunters, by now in full swing with X and Zero being the key players, are joined by Signas, Alia, and others help behind the scenes, and the Reploid known as Axl who has become a full-fledged Hunter. Axl is a prototype to a new generation of Reploids which can copy the appearances and abilities of other Reploids. By the time of Mega Man X8, such Reploids are being mass-produced. This can only result in chaos, and what humans remain are now attempting to flee to the moon, abandoning the earth to the mayhem that their Reploid creations caused.
For more information, check out the various game hint pages for details about the plots that this history lacks.