The Mega Man Killers, also known as the MKN (Mega Man Killer Number) series, are the robots created by Dr. Wily specially to eliminate Mega Man.
In some sources related to Mega Man: Dr. Wily's Revenge, Enker is designated as a "Mega Man Hunter" instead of "Mega Man Killer". Quint is not part of the MKN series, but serves an analogous role in Mega Man II.
Each Mega Man Killers made separate debuts in different games. It was not until Mega Man V that the three robots are together. Although very powerful, Either Dr. Wily or themselves made a fatal mistake of taking on Mega Man individually and was destroyed again separately.