Tyrant posted review (6)
I believe the answer is:
despot
'tyrant' is the definition.
(I know that tyrant can be written as despot)
'posted review' is the wordplay.
'review' indicates anagramming the letters.
'posted' with letters rearranged gives 'DESPOT'.
(Other definitions for despot that I've seen before include "Tyrannical dictator" , "Cruel and oppressive ruler" , "Posted (anag)" , "Tyranical dictator" , "Person with more than enough power" .)