Call I roguishly returned, discovering great ape (7)
I believe the answer is:
gorilla
'great ape' is the definition.
(gorilla is a kind of great ape)
'call i roguishly returned discovering' is the wordplay.
'discovering' indicates a hidden word (I've seen 'discovered' mean this (remove the letters covering the answer in the clue)).
'returned' is a reversal indicator.
'allirog' is hidden in the letters of 'call i roguishly'.
'allirog' backwards is 'GORILLA'.
(Other definitions for gorilla that I've seen before include "Ape - aggressive muscleman" , "thug" , "Big ape" , "Largest anthropoid ape" , "brutal man" .)