Robust defending judge, one revolutionary prophet (6)
I believe the answer is:
elijah
'prophet' is the definition.
(I've seen this before)
'robust defending judge one revolutionary' is the wordplay.
'robust' becomes 'hale' (in good health).
'defending' is an insertion indicator.
'judge' becomes 'j'.
'one' becomes 'i' (Roman numeral).
'revolutionary' shows that the letters should be reversed in order.
'j'+'i'='ji'
'hale' placed around 'ji' is 'hajile'.
'hajile' in reverse letter order is 'ELIJAH'.
(Other definitions for elijah that I've seen before include "Hebrew prophet in the time of Jezebel" , "Old Testament prophet" , "Mendelssohn oratorio" , "Hebrew prophet who rebuked Ahab and Jezebel" , "OT, Islamic prophet" .)