Robot Master is a name used to refer to human-like boss robots from the original Mega Man series that possess a very advanced level of artificial intelligence. Most, if not all, Robot Masters possess a Special Weapon. These powers can be gained mainly by Mega Man, Proto Man, or Bass after the robot is defeated.
Each Robot Master has a "consciousness", although the level of every "cognitive circuit" embedded inside each one of them varies, producing as many different "personality" types as found in people. Like humans, they can speak, and have emotional responses like shyness or anger. When Mega Man fights against a Robot Master, he takes great care to not damage their integrated circuit (IC) chip's "cognitive circuit". As long as the cognitive circuit isn't completely destroyed, they can be rebuilt any number of times.
The name "Robot Master" was first used in the North American instruction manual of Mega Man 3 in 1990, where it was used to identify the eight master robot bosses from the stage select screen, and continued being used until 1994, appearing in the manuals of Mega Man 6, Mega Man V and Mega Man's Soccer. In the first game's manual they were called "Humanoids" (a name later used for cyborgs in the Mega Man ZX series). In Japan they are known only as "boss characters", "Wily's robots", "Light Numbers", "Wily Numbers" and similar names.
Robot Masters generally have themes that fit their name, appearance, environment, minions, weapon and weakness. For example, Wood Man has a tree theme, giving him a wood-like appearance and a leaf-based power. His level is forest-themed, as are his robot underlings, and, like a tree, he is weak to fire and cutting attacks. Final bosses like King, playable characters like Bass, or support characters like Roll generally do not have such themes.