Possible Clues:

• Classic circus adjective
• Supreme as Ali claimed to be
• Most excellent
• Ali, per Ali
• Get stare from the mightiest
• Gee, that's about a trial, to a very large extent
• Mostly sounding like the fireplace, perhaps
• Nickname for 101-Down, with 'the'
• Biggest and best, like Muhammad Ali
• On radio, possibly Old Man River is most sublime