Original cast (for Seasons 1-3) included: Alan Alda as Benjamin Franklin "Hawkeye" Pierce, Wayne Rogers as "Trapper" John McIntyre, McLean Stevenson as Lt. Col. Henry Blake, Gary Burghoff as Corporal. Walter "Radar" O'Reilly, Loretta Swit as Major Margaret "Hot Lips" Houlihan, Larry Linville as Major Frank Burns, William Christopher as Father Mulcahy, and Jamie Farr as Corporal Maxwell Klinger.
In 1975 (end of Season 3), McLean Stevenson and Wayne Rogers left the show (their characters written out) and were replaced by Mike Farrel who played B.J. Hunnicutt and Harry Morgan who played Col. Sherman Potter. Larry Linville left in 1977 (end of Season 5) and was replaced by David Ogden Stiers who played Charles Emerson Winchester III. Gary Burghoff left in 1979 during Season 7 but re-appeared for one last episode in Season 8 before being effectively written out.
In 1983 the series finale of M*A*S*H called "Goodbye, Farewell, Amen" aired and it became the most watched TV episode in history.
After the show ended, producers came up with the idea of life after M*A*S*H and proposed it to the remaining members of the cast who wanted the show to continue. "After M*A*S*H" ran from 1983-1984 (one and a half seasons) and starred Morgan, Farr & Christopher in the setting of a veterans hospital Stateside. Gary Burghoff and M*A*S*H regular guest star Edward Winter (Col. Flagg) were the only two members of the original series that made guest appearances.
"After M*A*S*H" ratings were good to start off but to a sharp decline in the second season and the show was eventually canned.
These days, M*A*S*H is in reruns on TV all the time and many people still watch it.
McLean Stevenson was a regular guest host on the Tonight Show with Johnny Carson and in 1975 after numerous disputes with the M*A*S*H producers, he quit the show to start "The McLean Stevenson Show" (which unfortunately flopped). The character of Henry Blake was killed off at the end of the 3rd season.
Wayne Rogers was growing increasingly disgruntled throughout Season 3 over the fact that Trapper John was becoming a secondary character when originally he was supposed to have double billing with Hawkeye (Alan Alda). Rogers quit the show at the end of the 3rd season; therefore, there was no finale episode with him in it. It would be explained at the beginning of the 4th Season what happend to him.
Larry Linville quit the show after Season 5, feeling his character Franks Burns was becoming no more than the comedic foil for the show. Linville claimed there was nothing mroe for Frank Burns to do.
Gary Burghoff left the show due to personal and family problems in 1979.