Ruler exercises right in revolutionary European capital (7)
I believe the answer is:
emperor
'ruler' is the definition.
(I've seen this before)
'exercises right in revolutionary european capital' is the wordplay.
'exercises' becomes 'pe'.
'right' becomes 'r' (common abbreviation).
'in' indicates putting letters inside.
'revolutionary' says the letters should be written in reverse.
'european capital' becomes 'rome' (I've seen this before**).
'rome' back-to-front is 'emor'.
'pe'+'r'='per'
'per' put within 'emor' is 'EMPEROR'.
(Other definitions for emperor that I've seen before include "Eg, Caesar" , "Largest type of penguin" , "Sovereign - ruler" , "Beethoven's Piano Concerto No. 5 in E-flat major" , "eg Nero" .)