Possible Clues:

• Musical set in Oz, with "The"
• "The ___" (musical set in Oz)
• Best Musical Tony winner of 1975, with 'The'
• 1974 musical based on a 1900 novel, with 'The'
• 1974 musical based on a 1900 novel, with "The"
• Rap's ___ Khalifa
• Virtuoso, informally
• Expert, informally
• Adept expert
• "The __"