Ruler returning in anger as tyrant (4)
I believe the answer is:
tsar
'ruler' is the definition.
(tsar is a kind of ruler)
'returning in anger as tyrant' is the wordplay.
'returning' says the letters should be written in reverse.
'in' indicates a hidden word.
'rast' is hidden within 'anger as tyrant'.
'rast' in reverse letter order is 'TSAR'.
(Other definitions for tsar that I've seen before include "Word derived from Caesar, used by European rulers since 1547" , "Tyrant" , "Autocrat" , "Old Russian 22" , "Powerful man" .)