X is claimed to be the first reploid developed by Dr. Thomas Light. X was stored within a capsule for approx. 30 years until Dr. Cain discovered the capsule. X is a hero, and soon to be claimed as a legend, amongst the Hunters since he has been able to destroy Sigma seven times as well as stopping the Nightmare Incident who was led by Gate. X also delivered the final blow against Omega, took part in the Earth Reconstruction and helped stop the Limited Maverick War.

After the Limited Maverick War, X had retired from the Hunters, intending to live in peace in Northern America, but due to the recent problems and by the request of Bahamut, he rejoined and reassumed his command. His dream of Elysium, a world where humans and reploids can coexist in peace, was the inspiration for the Exodus to Mars and to create Elysium, the people's new home.
With this knowledge, X continues to lead the 17th Unit with renewed strength and confidence.

Even though he is part of the Maverick Hunters, X doesn't want to fight. Before the first Maverick War, he tried leading a peaceful life. However, X shows courage and leads the 17th Maverick Hunter Unit to halt the Maverick threat.

X's primary weapon is his X-Buster, which is able to obtain data from Mavericks he has defeated and have attacks based on that Maverick. The technology was duplicated during the Third Maverick War. X also wields the beam saber once held by Zero as a token of their friendship.

Throughout the Maverick Wars, X has gained help from his creator, Dr. Light. Within capsules, X has been able to get armor upgrades that improve his performance. The first four of these armors have been duplicated and Upgrades are available for the Hunters, however the other four armors cannot be duplicated because these are specifically designed to work with all four pieces.
The latest armor X has received, the 'Xavier' Armor (Not shown), seems to combine several abilities from past armors while at the same time, increasing his power and giving him a new Giga Attack, the Nova Crash.