Ruler in the throne room (4)
I believe the answer is:
nero
'ruler' is the definition.
(I've seen this before)
'in the throne room' is the wordplay.
'in' indicates a hidden word.
'NERO' is hidden within 'throne room'.
(Other definitions for nero that I've seen before include "Imperial Roman fiddler" , "Roman emperor who fiddled while Rome burned" , "Roman emperor infamous for his cruelty" , "Roman 9" , "Roman emperor on the fiddle?" .)