"MASH" was a TV ensemble show where characters came and went. How many characters stayed for the entire run of the show?

As long as the show ("MASH") aired, it maintained a relatively constant ensemble cast, with four characters — Hawkeye, Father Mulcahy, Margaret Houlihan, and Max Klinger — on the show for all 11 seasons. As Hawkeye Pierce, Alan Alda was the only series regular to appear in all 251 episodes. Several other main characters departed or joined the program midway through its run. Additionally, numerous guest actors and recurring characters were also used to help the show provide perspectives on the war, world, and people of the time.

In September 1972, based on a novel by Richard Hooker and a film that was a reasonable success, a TV series called "MASH" (the 4077th Mobile Army Surgical Hospital) premiered in America. It followed the lives of the doctors, nurses and staff of the hospital. As a TV series, it lasted 11 years (four years longer than the UN 'Policing Action' 2 in the Korean Peninsular that had inspired it).

Episodes in the series were both plot and character driven. Because of a plot or key characters, the show's tone could move from silly to sobering from one episode to the next. Dramatic tension would often occur between the civilian draftees of 4077th and the regular Army personnel — Hawkeye, Trapper John, B.J. Hunnicutt, etc. They were individuals who are forced to leave their homes in the U.S. to tend the wounded and dying of the war. They and other characters, such as Margaret Houlihan and Colonel Potter, represented ideas of patriotism and duty.