Maverick Hunters
X
X is the main protagonist of the series, as well as the character you control throughout the course of the game. He was created by the genius inventor, Dr. Light, sometime in 20XX, and may have been modeled after the original Mega Man. X was then found by Dr. Cain, an archaeologist in the year 21XX, after he uncovered the ruins of Dr. Light's former laboratory. Cain became fascinated with robots, and began to use X as a template to create even more like him. X now battles the Mavericks led by Sigma with his friend and fellow Maverick Hunter, Zero.
Zero
Zero is another protagonist in the series and close friend to X. Zero is a reprogrammed rogue who struggles to know his past and only fights to protect humans, as he still believes he is a threat to society. Together with X, he fights the Mavericks led by the rogue Sigma.
Dr. Cain
Dr. Cain is a human archaeologist who later became a robot expert after finding X. After awakening X, Cain invents Reploids, sapient robots based on X's design, with the most notable being Sigma. Once Sigma went rogue and gained enough loyal followers, Cain founded the Maverick Hunters, whose job it is to destroy the rogue Reploids, known as Mavericks.
Mavericks
Sigma
Original leader of the Maverick Hunters. Designed by Dr. Cain to be the perfect Reploid, Sigma was implemented with devices to protect him from turning Maverick. These devices failed and Sigma ended up as the leader of the Mavericks.
Vile
Vile is a recurring minor villain in the Mega Man X series, and frequently reappears as a mid-game boss. He has a distinctive helm with a T-shaped visor, bearing a striking resemblence to Boba Fett. Vile is introduced in Mega Man X, where he is a former Maverick Hunter now serving Sigma as his right-hand man.