Oscar Diggs

Emma, when she believed the Handsome Doctor was going to die without hope of regeneration, likened him to Father Christmas, the Wizard of Oz, and Scooby Doo. (TV: The Curse of Fatal Death)

referred to his previous incarnation as. (PROSE: The Secret Diary of the Master)

Behind the scenes
While he was only referred to as the Wizard of Oz in TV: The Curse of Fatal Death, this character's name is Oscar Zoroaster Phadrig Isaac Norman Henkle Emmannuel Ambroise Diggs, or Oscar Diggs for short. Also, it is not mentioned whether or not that, in the context of The Curse of Fatal Death, if the Wizard is fictional or not.