Inga (Mariette Hartley)
Soon Li Klinger
Edwina “Nurse Eddie” Ferguson (Arlene Golonka)
Captain Casey (the fake doctor)
Lt. Nugent (the nurse Radar fell for, played by Peggy Lee Brennan, who I went to college with.)
Just wanted to get that in.
Carry on. 
Aggie O’Shea, the reporter
Duke Forrest
“Painless” Woldowski
I don’t think they were on the TV show - or are we including the movie?
Charlie Lee (Jack Soo) the black marketeer.
(Hawkeye and Trapper trade Henry’s newly arrived antique oak desk to Charlie in exchange for medical supplies. Classic final scene of desk flying away by helicopter.)
There was that guy who, in several episodes, played the guitar. I don’t know if he was ever mentioned. It seems to me that he only ever appeared in episodes directed by Hy Averback.
Cpl. Spaulding, played by Loudon Wainwright III?
I never knew he had a name. I was often inebriated whilst watching MASH in college, were I first made the Averback/guitar playing guy connection.
Nurse Kelly.
Did anyone yet mention Rosie, proprietess of the just off-base saloon?
The thread title only referred to MASH characters, so I am taking them at their word. Other people have as well. “Spearchucker” Jones was only in the movie.
He was in the first season of the series, until the producers discovered that there were no black surgeons in the Korean War.
There was another guitar player, a dentist IIRC. He might have been in only one episode.
the orphans - i think they colletively count as one character
Recap:
Spearchucker Jones
Colonel Flagg
Dr Sidney Friedman
Benjamin Franklin “Hawkeye” Pierce
(Corporal)Sargeant Maxwell Q. Klinger
Corporal Lance Spaulding (played by Loudon Wainwright III)
Lt Col Donald Penobscot
Margaret “Hot Lips” (O’)Houlihan (she was more Irish in the movie)
Colonel Sherman Tecumseh Potter
Corporal Walter “Radar” O’Reilly
Captain Jonathan R. Tuttle
Maj. Charles Emerson Winchester III
Nurse Kelley
Five O’Clock Charlie
Lt Col Henry Blake
B.J. “Beej” Hunnicut
Seargent Elmo Zale
The helicopter pilot with diabetes
Fr. Francis Xavier Mulcahy
Double Dear John John from Reno, AKA Cowboy
Ho-Jon
Major Frank Burns
Rosie
General Douglas MacArthur (tho not a speaking role)
General Steele “Hey, hey, Uncle Bud, gonna beat my feet in the Mississippi mud!”
Sparky, friend of company clerks everywhere
Lieutenant General Robert “Iorn Guts” Kelly
Pvt. La Roche
Trapper John McIntyre
Marine Sgt. Marty “The Trenton Tornado” Urbancik
Lt Dish
Wendell Peterson
Inga
Soon Li Klinger
Edwina “Nurse Eddie” Ferguson
Captain Casey (the fake doctor)
Lt. Nugent
Aggie O’Shea, the reporter
Duke Forrest
“Painless” Woldowski
Charlie Lee
the orphans - colletively, they count as one character
that’s only 42, people. We can do better than that!
correcting typos:
Seargent Elmo Zale is Seargent **Zelmo ** Zale
Lieutenant General Robert “**Iron ** Guts” Kelly
(the perils of cut and paste) 
adding
Donna, aka Mrs Chuck Winchester
What? No mention of CAPT B.J. Hunnicutt?
Adam