The Wizard of Oz wasn't actually a crime boss, or even a criminal, although in the second book of the Oz series (The Marvelous Land of Oz), it is discovered that he earlier gave away a baby girl, Ozma, who was the rightful ruler of Oz, to the care of the evil witch Mombi, hoping to prevent the princess from returning when she was older, to claim her rightful heritage and usurp the Wizard's authority.

Perhaps the Wizard felt a sense of guilt about this past misdeed when he later met Dorothy, and it stirred him (after first charging the young girl to perform a hit on his enemy, the Wicked Witch of the West) to offer to take her home.

Frank Morgan, who appeared in somewhere close to 100 films in his long career, was already a well-known actor before he took on the personna of the Wizard in the 1939 movie, and though he is probably best known now for this role,  Morgan gave memorable performances in a number of classic pictures,  including The Affairs of Cellini  (1934---which garnered him an Academy Award nomination), The Great Ziegfeld (1936), The Shop Around the Corner (1940), and of course, The Wizard of Oz in 1939.

This is another nice casting clip provided by Cliffmount Pictures.