Horseman protecting lord repelled villain (7)
I believe the answer is:
riddler
'villain' is the definition.
(the Riddler is a Batman villain)
'horseman protecting lord repelled' is the wordplay.
'horseman' becomes 'rider' (I've seen this before).
'protecting' means one lot of letters goes inside another.
'lord' becomes 'ld' (abbreviation for the aristocratic title).
'repelled' is a reversal indicator.
'ld' written backwards gives 'dl'.
'rider' placed around 'dl' is 'RIDDLER'.
(Other definitions for riddler that I've seen before include "Sphinx?" , "One straining" , "passing on only the finest material?" , "Puzzle setter" , "Deviser of ingenious questions" .)