Possible Clues:

• See 13 Down
• In vain, I'd revised chapter for artist, scientist, and engineer
• Fictional code name
• Leonardo __, Renaissance polymath
• "Vitruvian Man" artist
• Helicopter inventor, it's said
• Dan Brown's 'The -- Code'
• Painter of the most expensive work of art, as of 2019
• Namesake of Rome's airport
• Having no time or energy, distractedly vindicate historical figure