One ancient imperialist gets about, born an athlete (7)
I believe the answer is:
ironman
'athlete' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'one ancient imperialist gets about born an' is the wordplay.
'one' becomes 'i' (Roman numeral).
'ancient imperialist' becomes 'rom' (I can't explain this - if you can you should give a lot more credence to this answer).
'gets about' means one lot of letters goes inside another.
'born' becomes 'n' (abbreviation, from the French 'nee').
'rom' going around 'n' is 'ronm'.
'i'+'ronm'+'an'='IRONMAN'
Can you help me to learn more?
(Another definition for ironman that I've seen is " Comic book character".)