Ruler exercises right in capital after revolution (7)
I believe the answer is:
emperor
'ruler' is the definition.
(emperor is a kind of ruler)
'exercises right in capital after revolution' is the wordplay.
'exercises' becomes 'pe' (Physical Education class).
'right' becomes 'r' (common abbreviation).
'in' means one lot of letters goes inside another.
'capital' becomes 'rome' (capital of Italy).
'after revolution' says the letters should be written backwards (letters revolve back).
'rome' back-to-front is 'emor'.
'pe'+'r'='per'
'per' put inside 'emor' is 'EMPEROR'.
(Other definitions for emperor that I've seen before include "Large colourful butterfly" , "Sovereign and richly-colored butterfly" , "A moth; a penguin" , "Large richly coloured butterfly" , "Tsar" .)