What is the name of Mega Man's sister robot?

Mega Man’s sister robot is named Roll.

Roll is a female support robot created by Dr. Light and is portrayed as Mega Man’s younger sister. Unlike Mega Man, who was converted from the laboratory assistant robot Rock into a combat robot, Roll was primarily designed for housekeeping and other domestic tasks. The sibling relationship is part of the series’ naming theme: “Rock” and “Roll” refer to musical terms.

Roll first appeared in the original Mega Man game, but her name was not explicitly shown until Mega Man 3, when she appears in Dr. Light’s robot roster during the ending. She became a recurring character in later classic games and other Mega Man media, often helping Mega Man between missions.

Players sometimes confuse Roll with Proto Man or Bass because all are major robot characters connected to Mega Man. Proto Man is Mega Man’s older-brother-like counterpart, while Bass is a combat robot created by Dr. Wily. Roll’s alternate versions, such as Roll Caskett and Roll.EXE, belong to separate spin-off continuities.