Mark Greene, M.D. is a fictional character from the American medical drama series ER. Portrayed by actor Anthony Edwards, he first appeared in the series' pilot episode, as well as subsequently appearing as one of the principal characters until the end of the eighth season. Edwards later returned to make a guest appearance in the fifteenth season episode "Heal Thyself".

ER is an American medical drama television series created by Michael Crichton that aired on NBC from September 19, 1994, to April 2, 2009, with a total of 331 episodes spanning 15 seasons. It was produced by Constant c Productions and Amblin Television, in association with Warner Bros. Television. ER follows the inner life of the emergency room (ER) of Cook County General Hospital in Chicago, and various critical issues faced by the department's physicians and staff.