Reploids are humanoid robots that are the major focus of the Mega Man series from the X series and onwards. Originally invented by Dr. Timothy Cain based on the technology of Mega Man X, the last creation of Dr. Thomas Light, Reploids are fully sentient artificial beings, capable of emotion and independent thought and action. Although sapient, Reploids during the Mega Man X series were still being created to fulfill specific roles and purposes. The technology developed by Dr. Cain also proved to be imperfect as Reploids frequently went "Maverick", causing all manner of violent crime and leading to some of the worst conflicts in the history of the planet.
During the time of the Mega Man Zero series, Reploids had become even more human-like. In Megaman ZX, Reploids and humans had begun to intermingle, with humans and Reploids becoming bio-cybernetic beings that were indistinguishable from one another (the only way to tell a Reploid from a human by then was the appearance of a small triangular symbol on their foreheads).