FearMonger

Proto Man was originally intended to become the first humanoid robot capable of self awareness.

He was a prototype robot, so his design was not complete. Although he greatly exceeded his creator's expectations on several levels, it was later discovered that his energy core had a critical problem that would eventually make him stop functioning. Dr. Light planned to repair him. However, since he was created too independent, Proto Man feared the modification would change his character. Proto Man refused to have Dr. Light meddle with his systems and fled to protect his sense of identity.

Dr. Light had presumed Proto Man to have died and regrettably gave up on him. Learning from his mistakes, he perfected the energy core and created two unit robots, Rock and Roll, to help him with the housework and other 6 robots destined to help humanity. Proto Man's design became the basis of the Sniper Joe series of robots. In Mega Man Powered Up, it is revealed that Proto Man despises the Sniper Joe series due to this.

Proto Man wandered the world alone. Before his energy reactor was completely depleted, the scientist Dr. Wily found him collapsed and dying. Dr. Wily managed to temporarily repair Proto Man by altering his power reactor from a solar to a nuclear one, as well as making other modifications, turning him into a combat robot. He also gave Proto Man the Proto Shield to compensate for his body's weakness, and in an attempt to hide his identity from Dr. Light, he gave him his helmet and his now-trademark visor. Working on Proto Man's systems gave Wily greater knowledge in creating robots at the same level as Dr. Light, helping his plans for world domination along.

Indebted to Dr. Wily, Proto Man served him until his encounters with Mega Man in Mega Man 3 made him realize his true nature. Proto Man saved Mega Man in the end of Mega Man 3, and officially turned against Wily in Mega Man 4, when he rescued Kalinka Cossack. However, he still refused help from Dr. Light, still holding onto his feelings. Mega Man doesn't know that Proto Man is his brother.

Proto Man's signature whistle is a staple of the character and almost always plays before his appearance.