The title role was written with W.C. Fields in mind. Producer Mervyn LeRoy wanted Ed Wynn, who turned down the role. MGM executive Arthur Freed wanted Fields, and offered him $75,000. Fields supposedly wanted $100,000. According to a letter from Fields' agent (which he claimed was written by Fields), Fields turned down the role to devote his time to writing the script for You Can't Cheat an Honest Man (1939). Since the role was perceived as being too small, additional roles were written for the actor in hopes of balancing the screen time for the actor playing the Wizard with that of the rest of the cast. Thus Frank Morgan plays the roles of the Wizard, Professor Marvel, the Gatekeeper, the cab driver with the "horse of a different color" who performs a musical number and the Wizard's Guard. It is also possible that Morgan was made up for the spooky projected image of the Wizard's face transposed on the billowing steam in his Throne Room.