Mandela is a naval hero (6)
I believe the answer is:
nelson
I believe this is a double definition.
'mandela' is the first definition.
(I know that mandela given name Nelson)
'naval hero' is the second definition.
(I've seen this before)
'is a' acts as a link.
(Other definitions for nelson that I've seen before include "Lancashire town" , "Lady Hamilton's naval lover" , "Victorious flag officer" , "Admiral; wrestling hold" , "Lady Hamilton's navy lover" .)