X was designed and created by Dr. Light to be a robot who could think and make his own decisions without programming limitations. Unique among all of Dr. Light's creations, X possessed incredible physical and reasoning capabilities. However, Light feared that, since X didn't have any moral programming to dictate his morality or actions, he could become a grave threat to the world. Therefore, he sealed X away into a special capsule that would test his systems in a myriad of scenarios designed to ensure that X would be able to discern right from wrong and be always willing to do the right thing. Apparently, this process would take more than 30 years, and Light was very old and would not live to see X leave the capsule and enter the world. He left a warning on the computer in the lab he placed the capsule in and ordered anyone that may find the capsule to not release the robot within until his testing was complete.

Maverick Hunter X, the 2006 remake of the original Mega Man X, shows a slightly different series of events. The Day of Σ, an unlockable prologue OVA included on the UMD, shows Dr. Light speaking with X several times during his creation, while in the SNES game Light sealed X away without activating him once. Furthermore, Light's intention of sealing X was different in Maverick Hunter X. Instead of fearing that X would become a threat because of his immaturity, Light feared that it would be the humans who were immature and not ready to live together with a robot as similar to a human as X would be by the time he finished his work. Instead, Light wanted him to fight for the people of the future and guide them to peace and happiness.

X is a hot-blooded, committed, and strong-willed Reploid who has little tolerance for injustice. Though X fights with all his might against Sigma and his Mavericks, he is a pacifist at heart, something he might have inherited from the original Mega Man or Dr. Light. X would like nothing more than the fighting to be over, and for humans and Reploids to coexist peacefully next to each other, like his creator had always wished. He cares deeply for the victims of the war and for his friends who've fought so long with him, especially Zero, whom he regards as his best friend. X is easily frustrated when things go awry and rarely seems to understand the true motives of Sigma and other Mavericks

Although he's constantly conflicted with the battles he must fight, he eventually begins to come to terms with it and understands that he must indeed fight for the peace he desires to be a reality. This change is best seen during the Zero series in where the relationship between the two is reversed as it is X the one who actually supports Zero and encourages him to fight when either confused or doubtful in his actions.

X's creation by the hands of Thomas Light began at some point during the later days of the original Mega Man series, specifically, sometime after Mega Man 10,[3] but no exact dates were given. Unlike most robots of his time, X was created with a unique system akin to that of a conscience, that allowed him to think, feel and act completely on his own, and highly advanced mechanics that far surpassed anything of the current day. The purpose of X's construction and birth was in the sake of Light's dream, of one day giving robots the ability and freedom to evolve and grow in the exact fashion of all living beings.

However, Light was not without foresight and fears for his ultimate project. Though X was now akin to that of a living, sentient being with their own free will, but with a physique that of a strong and powerful machine, Light feared he could grow instead to be a potential threat to the world. In addition to X's immaturity stemming from his inexperience that could lead to misunderstanding or even catastrophe amongst a world unknown and new to his existence, Light was nearing the end of his life with no successor to continue his work, concerned with how the people of the future would ever properly receive X, and that X faced an unknown future filled with such possible dangers and hardships that Light would not be able to console and guide him through.

To test the reliability of his learning and morality, Light prepared a stasis capsule that would perform system tests on X's circuits and AI to prove his maturity, that would take approximately 30 years to complete. With nothing but his love and compassion long put into his work throughout his life, left to be carried on by future generations, Light addressed his final words, of his hopes, wishes, fears, and dreams, for X to bring peace and to fight for the people of the future. On September 18 20XX, readying all last preparations, Mega Man X was sealed away.

The sleeping robot eventually passed all tests the capsule had prepared for him and he was found in the year 21XX (possibly in the year 2114 or later, according to the log of Cain's PC in the opening of Mega Man X, 100 years after X was sealed by Dr. Light) by scientist Dr. Cain. Cain, not being an expert in robotics, was baffled by the design specifications Light had included on the computer as even a century later they were ahead of anything the world had ever seen. From these specifications and with the help of X, Cain began developing his own version of next-generation robots, which came to be known as Reploids. However, the Reploids never received the same ethical testing as X. Apparently because of this oversight, over time more and more Reploids began to act strange and, eventually, become violent against humans and even other Reploids. These Reploids were deemed "Maverick" (Irregular in Japan) and, as incidents of Reploids going Maverick increased, the human government decided to found a department which was supposed to deal with the Mavericks, the Maverick Hunters.

Feeling responsible for this situation, X joined the Maverick Hunters and became part of Sigma's 17th Elite Unit. While other operatives such as Sigma and Zero were elevated to the higher classes, X remained at B-class. This was most likely due to a tendency in X to hesitate in battle instead of fully committing. This tendency caused other Maverick Hunters, such as Vile, to look down on X as weak. It has been noted, however, that X has "limitless potential" should he choose to access it (according to Cyber Peacock in Mega Man X4), and that Sigma, Zero, and Dr. Cain have all seen his potential from the beginning.

The Day of Σ
While X was a member of Sigma's Elite Hunter Unit 17, he befriended many other members of this unit, particularly the S-A class hunter Zero. The Hunters were busy though, as giant Mechaniloids (robots less intelligent than Reploids) began attacking Abel City. The Maverick Hunters were baffled as to who was behind the attacks. During one of the battles against the berserk Mechaniloids it became apparent to Sigma that X would refuse to use his weapons if an ally was in danger. After speaking to Dr. Cain, Sigma discovered that his worrying is what makes him so advanced. It was then that Sigma became obsessed with X.

X and Zero began investigating these events to discover the hacker causing Mechaniloid outbreaks throughout Abel City. The two hunters traced the signal being sent to the Maverick Mechailoids, where they discovered that the hacker responsible for the rampaging Mavericks was none other than Sigma. X and Zero fought Sigma, but were damaged in the encounter, allowing Sigma to escape, although not before X, with some of his limitless potential awakened, burned Sigma's characteristic scars onto his eyes. Sigma eventually turned his lieutenants Maverick, and launched an attack against Abel City, leading into Mega Man X.

Mega Man X/Maverick Hunter X
Mega Man X
MegamanMHX
Mega Man X, as a boss in Vile Mode in Mega Man Maverick Hunter X.
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Maverick Hunter X is a re-telling of the original Mega Man X story, and while the former seems to deviate on a few topics, it is generally true to the idea of the latter.

It starts with X who is dealing with Maverick activity along the Central Highway, part of Abel City where the characters live. As he goes about fighting off hordes of Mechaniloids, he meets Vile, who has apparently gone Maverick, and confronts X in his special Ride Armor.

X battles Vile, but ultimately is defeated, and taken captive. X is saved by Zero, who blasts the Ride Armor's arm off with a single charged shot. After Vile retreats, X laments at his inability to defeat the war Reploid. Zero consoles X, telling him that he still has much potential to be unlocked.

X then faces the eight 'leaders' of Sigma's Maverick armies. One by one, he battles them, defeats them, and obtains their special weapons.

Once the eight bosses are destroyed, X is informed that Zero has finally discovered the whereabouts of Sigma's fortress.* They discuss their method of assault. Zero tells X he will barge in the front to draw the enemy's attention, and suggests X find another, safer way in. During his journey throughout Sigma's Fortress, X confronts the eight bosses yet again And, as before, he defeats them to move onward.

In the original game, X actually meets up with Zero outside said fortress. In MHX, however, X simply receives a communications from Zero, who is already working his way inside.
In the third section of the fortress, X reaches a small hallway where he sees that Vile has successfully defeated Zero, and must battle the war-machine once more to rescue him. At first, he is once again overwhelmed by Vile's powerful Ride Armor,* but it is at this point where Zero gets his second wind, leaps on the machine from behind, and destroys the ride armor in a desperate attack.* This utterly destroys the Ride Armor, although leaving Vile unharmed. Still, X can now battle on more equal ground with Vile, and defeats him after a tenuous battle. He then rushes to Zero, who is in such critical condition that he urges X to leave him behind, and fight Sigma in his stead. With much regret, X marches onward to fight Sigma.

In the original game, X had to fight another losing battle to Vile's Ride Armor. In MHX, this battle is skipped, as Vile captures him by surprise. Zero destroys it while he is distracted with X.
There seems to be confusion as to how Zero destroyed the Armor. Some believe a charged-shot at point blank, while others still argue a self-destruct or overload of the Buster in question. The latter seems more likely, considering the damage he suffered as a result, which would not have happened with a simple charged shot. However, both will support the storyline depending on whether X has obtained the Buster Upgrade from the Dr. Light Capsule in Flame Mammoth's Stage: The theory of Z-Buster overload applies when X has obtained his own Buster Upgrade prior to the Vile battle; while the Z-Buster charged shot theory applies when X did not obtain the Buster Part, allowing Zero to give his own Z-Buster to X as a Part Upgrade with the same Charged Shot as what Zero has himself with the ability to charge Special Weapons.
X finally reaches the boss chamber where Sigma resides. They have a brief exchange, and Sigma congratulates him for "making it this far", but then comments that he will put X to a little test before engaging the hunter himself. X is then forced to fight Sigma's dog, Velguarder. After destroying the guard dog, Sigma throws off his cloak and fights X head-on with his beam saber. X eventually defeats Sigma, but as his body exploded, Sigma's head is snatched up by a cable from somewhere in the background, which pulls it into a much larger body, which lights up and reveals a menacing wolf-body that attacks X, nearly taking up the entire room. X fights Sigma and defeats him again, causing the fortress to collapse. X manages to get out in time and watches the fortress collapse as he contemplated his actions, and his future.

Mega Man X2
Picking up where Mega Man X left off, the Hunters have tracked down the remaining Mavericks. The X-Hunters, a group of Mavericks who wish to destroy X, gather the parts of Zero's corpse, seeking to use them as bait to lure X to his destruction. X destroys the X-Hunters and gathers Zero's parts, eventually discovering that Sigma was behind the plot all along. If the player gathers Zero's parts before assaulting Sigma's HQ (at the North Pole), Dr. Cain says he still has Zero's microchip and can rebuild him, but it will take some time. Before reaching Sigma's lair, X is confronted by an evil, black Zero clone. The real Zero arrives and destroys it with a powerful combination attack. The player can choose to ignore the X-Hunters; in this case, a brainwashed Zero shows up, which has according to Sigma's words a grudge against X for not rescuing him from the hands of Sigma's lackeys. After being beaten, Zero comes to his senses and rejoins X and the Maverick Hunters, but plays no further part in the game (this ending is considered non-canonical, as it is not reflected in later games). X confronts and destroys Sigma once again, while the newly-rebuilt Zero destroys Sigma's central computer.

Mega Man Xtreme
Set between X2 and X3, a hacker named Techno has invaded the Hunters' Mother Computer and is using the data of previous Mavericks against the organization. With the help of Middy, X goes into cyberspace, where he discovers that Sigma had "influenced" Techno. X accidentally destroys Techno, then learns that Middy is Techno's twin brother, and that destroying Techno destroyed Middy as well. X, crushed, challenges Sigma once again and defeats him, extracting a measure of vengeance.

Mega Man X3
There has been a period of peace after a Reploid scientist named Dr. Doppler created a supposed cure for the Maverick Virus. This cure turns out to be an ineffectual placebo, however, and the Maverick Hunters find themselves overwhelmed with a massive Maverick uprising. X and Zero enter the fray and discover that the virus and Sigma are one and the same, explaining why Sigma keeps coming back. X and Zero destroy Sigma's new battle body (built by Doppler, who had been infected with the virus). It is revealed, but unbeknown to X, that his ultimate fate to save the human race would be to destroy Zero. This is a mildly misleading translation from the Japanese version, which merely says that X knows in his heart that he is destined to fight Zero.

Mega Man Xtreme 2
Set sometime after X3 and before X4, X and Zero head to Laguz Island, where they battle the Soul Erasers, Berkana and Gareth. X defeats Berkana and Zero defeats Gareth, and the two team up to defeat Sigma.

Mega Man X4
The Repliforce, an organization that acts as an ally to the Maverick Hunters, were branded Mavericks after they were accused of the incident where the floating city Sky Lagoon is destroyed and falls to the ground, starting the Repliforce War. X, though, was led away from the real targets by a spy of Sigma named Double, and it was Zero this time who hunted down the Repliforce commanders, killing his good friends Colonel and Iris in the process. X, realizing that he was tricked and discovering that Sigma had set up the entire plan, became very frustrated and swiftly disposed of Double. After beating Sigma, however, he was beginning to doubt his ability to remain sane. He told Zero that if he ever were to go Maverick, that Zero would have to destroy him.

Mega Man X5
Mega Man X
Ultimate ArmorX
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Ultimate Armor
With peace restored, the Hunters hire several new officers, including Alia. Unfortunately, X gets into a confrontation with the Sigma Virus, accidentally spreading it all over Earth. This turns out to be yet another of Sigma's evil schemes. In addition, Sigma attempts to send the space colony Eurasia into the Earth, thus spreading the virus further, in order to awaken Zero's true self.

A large energy readout of the Eurasia colony returned a signature that it was infected with the Sigma Virus, so the Maverick Hunters saw no other solution except to alter the colony's path by striking it with a blast from the Enigma laser cannon. The Enigma laser cannon fails to destroy Eurasia, so Signas comes up with another plan, to launch a Space Shuttle directly at the colony to destroy it. Zero pilots the shuttle and crashes it into Eurasia, which successfully destroys it (there is another story possibility; however, Eurasia being destroyed is canon).

However, a new virus appears, called the Zero Virus, and X and Zero have to find the source.

X faces off with Zero after he ignored orders to report back to Base for a full physical check on his virus readings, and the two are knocked out during the battle. Sigma appears and Zero saves X from him. The two then go on to confront Sigma. This is the canon storyline.

In the other story possibility, the overwhelming amount of the virus becomes a catalyst that exposes Zero's true self.

Sigma reveals to X that Zero's true form is the one that emerges when he is powered up with the Maverick Virus (this mechanic is also reflected during gameplay). As it turns out, Zero was the one who had spread the virus to Sigma during their first confrontation, as shown in a cutscene during Mega Man X4. Sigma also speaks of a mysterious new ally who built a body for him. He also says that this person is interested in Zero "as if he was his own father" and claims that he and X know each other well, because they were enemies in the past (obviously referring to the character Dr. Wily from the Mega Man series).

Once beaten, Sigma claims he will take Zero down with him. As X and Zero both lay damaged from Sigma's massive explosion, X stands over Zero's battered body, hoping for signs of life. Sigma's remains then fire a blast straight through X and Zero. Zero revives for just a moment, destroying Sigma's remains with a blast from his Z-Buster and then passing away. X was badly injured, but a hologram of Dr. Light appeared and miraculously repaired him. The next scene shows X holding Zero's Z-Saber and going off on another mission, stating that with Zero's blade, he can fight any enemy.

Being a robot, X possesses strength, speed, endurance and other abilities well above the normal human capacity, although his physical limits are never revealed in the games. He can performs various specially defaulted actions like Dash, Wall Kick and Air Dash. He also has upgrades in which completed set are armors. The true scope of X's abilities are constantly under speculation by many of the characters in the series. X seems to constantly change and evolve. In many instances he seems to draw on some unknown power within himself. Both Dr. Cain who examined X as well as Sigma who is obsessed with X and Zero's capabilities don't understand a large portion of how both Hunter's internal systems work. What is known is that these hidden abilities make X immune to the Maverick Virus and let him match any opponent. It is also likely that the armor that Dr. Light left him may be tools that allow X to slightly tap into his "limitless potential". It can then be assumed that X's true power is capable of release only on his standard frame. However, this only happened during X's fight with Sigma in the last chapter of "The Day of Σ", and only for a moment due to the damage received from Sigma.[7]

Plasma Shot: The X-Buster, focuses solar energy from X's fusion reactor into a plasma bullet that causes physical damage upon impact.
Variable Weapon System: Like the original Mega Man before him, X has the ability to adapt the weapons systems of powerful Reploids that he has defeated into weapons he can use. These weapons come in many varieties, often providing additional mobility as well as offense. Of course, the Mega Man series convention of janken applies, and each boss character is weak to a different boss character's copied weapon.
Upgrades: X can take on various upgrades like X's armors, chips to complete an armor set, significantly increase his power at an instance, with none or little drawbacks. Complete armors can perform powerful Giga Attacks.
Giga Attack: Since Mega Man X2, every game except X3 has a Giga Attack for most of X's armors. Most Giga Attacks starts at full gauge when entering any stage and the only way to refill its energy is by taking enemy hits and/or attacks. Also, Giga attacks usually freeze all action as X attacks all enemies that are on-screen.