Greek hero longs to curb evil (8)
I believe the answer is:
achilles
'greek hero' is the definition.
(I've seen this before)
'longs to curb evil' is the wordplay.
'longs' becomes 'aches' ('ache' can be a synonym of 'long').
'to curb' indicates putting letters inside (curb can mean to restrain or contain).
'evil' becomes 'ill' (I've seen this in other clues).
'aches' placed around 'ill' is 'ACHILLES'.
(Other definitions for achilles that I've seen before include "Famous Greek" , "Homeric hero" , "Greek hero (with heel and tendon)" , "Ancient Greek hero" , "Ancient soldier" .)