The Wizard's full original name was (deep breath) Oscar Zoroaster Phadrig Issac Norman Henkle Emmanuel Ambroise Diggs. When he grew up, he shortened this unwieldy name to Oz - after all, would you want your initials to be O.Z.P.I.N.H.E.A.D.? While working as a stage magician, ventriloquist, and balloonist for a circus, an accident brought him to Oz. Since the balloon had his abbreviated name - also the name of the land - on it, all the residents assumed he was the new ruler.

As revealed in Dorothy and the Wizard in Oz.