Proto Man is a major character in the Mega Man, series, acting as a recurring support character. In the Ruby Spears cartoon adaptation of the game, Proto Man was changed into a evil rival character.
Proto Man was originally a prototype robot created by Dr. Light and Dr. Wily. However, due to a malfunction, Light asked Wily to destroy the plans, but Wily secretly kept them to himself. When Wily turned to evil, he finished the robot, thus creating Proto Man. While Proto Man follows Wily's plans and serves as his right hand, he isn't exactly loyal, as his only goal is to prove himself superior to his brother Mega Man.
Proto Man's role in the cartoon is very similar to that of Bass in the games. In fact, had the series continued the creators planned for Proto Man to reform and for Bass to take his role as the rival character.