Eastern politician, Queen or ruler (7)
I believe the answer is:
emperor
'ruler' is the definition.
(I've seen this before)
'eastern politician queen or' is the wordplay.
'eastern' becomes 'e'.
'politician' becomes 'mp'.
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'e'+'mp'+'er'+'or'='EMPEROR'
(Other definitions for emperor that I've seen before include "Roman leader" , "Tsar" , "noted by Beethoven" , "Sovereign and richly-colored butterfly" , "Character in 24 ac" .)