Roman god: he's cruel, unfortunately (8)
I believe the answer is:
hercules
'roman god' is the definition.
'he's cruel unfortunately' is the wordplay.
'unfortunately' indicates an anagram.
'hes'+'cruel'='hescruel'
'hescruel' anagrammed gives 'HERCULES'.
(Other definitions for hercules that I've seen before include "Mighty hero of Greek mythology" , "labourer" , "Strong hero" , "One who laboured" , "Mythical strongman - he's cruel (anag)" .)