Mad dictator imprisons fanatical devotee (6)
I believe the answer is:
addict
'fanatical devotee' is the definition.
(I've seen this before)
'mad dictator imprisons' is the wordplay.
'imprisons' indicates the answer is hidden within the clue (I've seen 'imprisoning' mean this (the answer is imprisoned within the clue)).
'ADDICT' is hidden in the letters of 'mad dictator'.
(Other definitions for addict that I've seen before include "Habitual drug user" , "Person compulsively given to taking drugs" , "One hooked on drugs" , "Victim of habit" , "One dependent on drugs" .)