Hun leader (6)
I believe the answer is:
attila
'hun leader' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for attila that I've seen before include "Well-known Hun" , "Great king of the huns" , "Hunnish conqueror" , "Fifth century Hunnish leader" , "5th century king of the Huns who sacked Rome" .)