Proto Man is considered to be the "older brother" of Mega Man since he was created before him as a prototype combat robot. Because of his mistrust of Dr. Light, Proto Man decided to escape from Dr. Light's Lab.
As he was the first robot created by Dr. Light, Proto Man had an imperfect core. This caused him to break down while wandering the world. Dr. Wily later found, reprogrammed, and repaired Proto Man, which in turn gave Wily a better knowledge of robots to further his plans for world domination. Proto Man felt indebted to Wily, so he served him under the alias "Break Man" until Mega Man 3 wherein he discovered the true purpose of Wily and decided to help Mega Man instead (but not Dr. Light).
To date, he still has not forgiven Dr. Light, and constantly criticizes Robot Masters created by Dr. Light in Mega Man Powered Up if they are unfinished.
Proto Man originally appeared in Mega Man 3 as a mysterious miniboss. He became the boss "Break Man" later in the game. In the end, Proto Man saves Mega Man, and Dr. Light explains to Mega Man who Proto Man was.
In Mega Man 4 Proto Man rescues the kidnapped Kalinka and brings her to Mega Man and her father, Dr. Cossack, after Mega Man defeats him, to let her tell Mega Man that her father was forced to work for Dr. Wily.
Proto Man made a reappearance in Mega Man 5 as the alleged antagonist of the story, but in reality, the antagonist was Dr. Wily.
In Mega Man 6 Proto Man appears in Tomahawk Man's stage to give Mega Man the Energy Balancer upgrade.
In Mega Man 7, Proto Man is a secret boss and an NPC with helpful tips.
Proto Man is a story character in Mega Man 8 and Mega Man & Bass.
Mega Man 9 and Mega Man 10 mark his primary playable versions. In Mega Man 9, Proto Man is a downloadable character with the ability to slide and charge his Buster. He is the same in Mega Man 10, but instead of being a downloadable character, he is available straight away. The new downloadable character was Bass.
Proto Man is a playable character in the arcade games Mega Man: The Power Battle and Mega Man 2: The Power Fighters. In Mega Man: The Power Battle, Proto Man was overall the same as Mega Man. In Mega Man 2: The Power Fighters, Proto Man was different from Mega Man and Bass due to each of the characters having a special attack, and Proto Man's was the "Proto Strike", a large flare shot out of his Proto Buster.
Proto Man is the secret character in Mega Man Powered Up, unlocked by clearing all Challenges or downloading a file. Proto Man is superior to all other characters in every aspect except defense. He has his Proto Strike again, which is the same as a charged Mega Buster except the attack does not shoot through tiles; the Proto Shield which can save him from taking damage, but must be collected every time the Proto Shield is struck; and a much higher jump, making every secret area easier to explore. Unlike Mega Man 9 and Mega Man 10, Proto Man does not have an ability to change his weaponry; he can only utilize the Proto Buster shot.
A Proto Man costume can be collected and worn by Frank West in Dead Rising 2: Off The Record. Large cardboard cutouts are also frequently seen littered around Dead Rising 2's Fortune City.