Mega Man is a highly advanced robot with a near-human personality created by Dr. Thomas Light. In the year 200X, Dr. Light and Dr. Albert Wily worked together to create robots with unprecedented artificial intelligence that could be used to supervise other less advanced robots. The prototype of these robots was known as Proto Man (also called Blues), but having a free-spirited personality, and fearing being tampered with to fix an unstable core, he ran away. Dr. Light theorized that Proto Man ran away because he desired a companion, so he next designed two robots: Rock, designed as a lab assistant, and Roll, designed for house work. Based on these successes, Light and Wily then built six Robot Masters: Cut Man, Guts Man, Ice Man, Bomb Man, Fire Man, and Elec Man. However, Dr. Wily grew jealous of the recognition Light received for their work. Wily began his designs for world conquest and stole the Robot Masters. Seeing Rock and Roll as useless, Wily left them behind, inadvertently creating his ultimate undoing, as Rock would volunteer to be converted into a fighting robot. As Mega Man, he would thwart Wily's plans time and time again.
As Mega Man, Rock possesses the Mega Buster, a weapon that converts his hands into a powerful energy cannon. From Mega Man 4 onwards until Mega Man 9, the Buster can be charged to release a Charge Shot. Beginning in Mega Man 3 and again continuing until Mega Man 9, he also possesses the ability to slide along the ground. Mega Man's most impressive power, however, is his Variable Weapons System, which allows him to copy the powers of Robot Masters he defeats. These weapons then prove useful for taking out smaller enemies or another Robot Master weak to that particular weapon in a rock-paper-scissor style system.
Mega Man is consistently shown to have a strong sense of justice, highly valuing peace. These values were what led him to be converted into a fighting robot in the first place, and the games stress Mega Man's never-ending fight to ensure peace. However, Mega Man has his breaking point, as seen in Mega Man 7 where he nearly kills Dr. Wily, tired of his repeated attempts at world domination.
Mega Man has a large group of allies and companions who help him on his adventures. Dr. Light and Roll often serve in an advisory capacity, while other robots help him more directly. Rush, Mega Man's robotic dog, serves as transportation for him by transforming into tools such as a spring or jet. Proto Man often aids his younger brother after a stint of working for Dr. Wily in Mega Man 3. Other less advanced robot helpers include Eddie, who distributes items, Beat, who serves a variety of functions, and Auto, another assistant of Dr. Light's.
Mega Man appears as a playable character. He uses copied special weapons from Robot Masters that he fought in the original series. Thus, his combat is more focused on weapon and ranged based rather than physical combat, in vein to Snake.
Super Smash Bros. for Nintendo 3DS trophy descriptions