So Morgan is credited for 5 roles in Wizard of Oz. 1939.
Why yes, I am watching the Wizard of Oz on Easter.
Alec Guinness played 8 different characters in Kind Hearts and Coronets.
Ten years later.
Never mind, I didn’t read the OP title carefully enough.
The Playhouse by Buster Keaton
Only Me (1929) - Short film in which Lupino Lane plays 24 roles.
The One-Man Band (1900) - Short film in which George Melies plays 7 roles.
Seven Faces (1929) - Paul Muni plays 7 roles.
Sounds like The One-Man Band (1900) has to be the winner, thank you.
Tony Randall played 7 roles in “The 7 Faces of Dr. Lao.”
Which was well after, that list is large.
[Must read more closely.]
I misread that as Frank Oz. That’s what I get for skimming.
I think it is easy to do, I’m pretty sure Frank OZ was not a part of the awful Muppet Oz Movie. For that I am thankful.
Technically he only played 2 roles-the other 3 were the Wizard in disguise, playing all of his minions.
He is listed for 5 roles, so hard to say. Logistically it doesn’t even make sense anyway. The final doorman is very hard to reconcile as being the Wizard.
I checked imdb to see what roles he was credited with. It says "Professor Marvel/The Gatekeeper/The Carriage Driver/The Guard/The… " and then it cuts off. And I was annoyed that I couldn’t see what the fifth one was, but then I figured it out pretty quick. 
Wikipedia also lists him for 5 roles as did Rotten Tomatoes. I figured if those 3 agree, as did the credits themselves. It is 5 roles.
That’s been a question of mine forever. Are they intended to be the same guy?
Tom Hanks played at least six roles in The Polar Express.
It was filmed in motion capture. Requiring Hanks to perform and do the voices.