Stopped heartless revolutionary dictator (6)
I believe the answer is:
despot
'dictator' is the definition.
(I know that despot is a type of dictator)
'stopped heartless revolutionary' is the wordplay.
'heartless' means to remove the middle letters.
'revolutionary' indicates anagramming the letters.
'stopped' with its centre taken out is 'stoped'.
'stoped' with letters rearranged gives 'DESPOT'.
(Other definitions for despot that I've seen before include "Tyrannical dictator" , "Cruel absolute ruler" , "Posted to tryant" , "Posted by tyrant" , "Possibly 4 [CZAR]" .)