Ace fellow is a looker (6)
I believe the answer is:
adonis
'a looker' is the definition.
(I have seen 'male looker' mean 'adonis' so perhaps 'looker' could also mean 'adonis')
'ace fellow is' is the wordplay.
'ace' becomes 'a' (abbreviation).
'fellow' becomes 'don' (both can mean an academic).
'a'+'don'+'is'='ADONIS'
(Other definitions for adonis that I've seen before include "Handsome Greek loved by Aphrodite" , "Archetype of male beauty" , "lovely chap" , "striking youth" , "Aphrodite loved this beautiful youth" .)