Actor Frank Morgan played five different roles in The Wizard of Oz: 

In the Emerald City, he was the cabby who drove the Horse-of-a-Different-Color, 
a guard at the entrance to the Wizard's palace, 
the doorkeeper at the Wizard's palace, 
and the Great and Powerful Oz himself; 

in the Kansas sequences that opened the film, 

Morgan portrayed the disreputable Professor Marvel.