Observe Russian ruler being declared an emperor (6)
I believe the answer is:
caesar
'emperor' is the definition.
(title used by Roman emperors)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for caesar that I've seen before include "Top man" , "leader who acts like a dictator" , "Old Roman emperor like Julius" , "Roman dictator" , "See 12" .)