Zero is one of the main protagonists from Capcom's Megaman X and Megaman Zero series.
Zero was created by the late Dr. Albert Wily sometime in the early-21st century. His first chronological appearance was in the form of schematic blueprints during Bass's ending for Mega Man 2: The Power Fighters and described by Wily as his "greatest masterpiece." Learning from his past mistakes, including the accidental creation of Bassnium, and his construction of Bass and King, Wily constructed a new robot, far more advanced than anything he had ever built before with a power level far superior to that of Bass or Mega Man. Wily took the time to complete Zero, originally planning to use him against both Mega Man, and his insolent rebellious Bass. However, this never happened, and he was never utilized during the Wily Wars. Zero was routinely activated in a semi-conscious state during his construction, and Wily conversed with him, mirroring what Light himself did with X. Zero was aggressive and disobedient, and because of this Wily decided to seal him in a capsule. Decades later, in the early 22nd century, he was awakened by a group of Reploids prior to the first Mega Man X game. When he was first activated, he awoke as a Maverick (by the definition of wanting to cause harm to all humans) and destroyed all intruders who had dared to enter Wily's lair. Zero was later cornered by Maverick Hunter Elite, Gamma's Maverick Hunter unit inside an unknown facility, however at the cost of a total loss of said unit. Not wanting to get anymore comrades endangered by the powerful enigmatic Maverick, then-Hunter Commander Sigma himself challenged Zero in a fateful one-on-one battle. Even though Zero eventually gained the upper hand during the battle, Sigma was able to defeat the red Maverick after the gem on Zero's head began to glow and a 'W' symbol appeared, apparently causing Zero great pain. Sigma punched this crystal, shattering it and defeating Zero (subsequently passing on the Maverick Virus to himself). He was then brought to Dr. Cain, who analyzed him. After that, Zero recovered from his battle with Sigma and was placed under Sigma's watch. Zero did not show any signs of Maverick behavior and was enlisted into the Maverick Hunters' 17th Elite Unit.
Zero had sacrificed his life multiple times as a Maverick Hunter and was usually rebuilt or repaired as soon as possible. However, towards the end of the Maverick Wars and near the beginning of the Cyber Elf Wars, Zero was defeated and left in a century long hibernation before being awakened by Dr. Ceil in an even more distopian future. Zero quickly joined a resistance movement which fought against injustices brought about by an imperfect copy of X, who ordered the mass execution of hundreds of reploids due to an energy crisis. After the fall of Copy X, Zero witnessed the releasing of the Mother Elf and the rise and fall of the genocidal maniac Dr. Weil.
The ultimate result of the infamous Dr. Albert Wily's research, Zero was built with the intention of surpassing anything Wily had built before, and to destroy his long time nemesis's creation, Megaman, as well as his own misguided creation, Bass. Being made before the introduction of standard mass produced Reploids and during the construction of X, his internal processes and construction are considered to be more advanced than most known robotics and on par with X's parameters and capabilities.
He is initially outfitted with an armament known as the Z-Buster, an arm cannon capable of firing of blasts of energy as well as manipulating it to launch it in special variations and projections.
During the X2 series and onward, Zero adopts and becomes the user of the Z-Saber, a beam sword not unlike a lightsaber in certain aspects, and is his trademark weapon. Not only capable of manifesting itself as a beam of light, it is also capable changing its energy patterns to manifest in different colors, states of energy such as fire and ice, and even into various masses and metal.
Zero is also outfitted with the Learning System, a system not unlike the Variable Weapons System in its copying and adaptation of certain weapons, but adapts various abilities and techniques of opponents and enemies, and even goes as far as copying the kind of power emitted from the attack, should it have energy projection.
However, underneath his exterior displays of ability and power, just like X, Zero holds an immense and potentially limitless capability for adaptation and power.