Keen man deposing leader (4)
I believe the answer is:
avid
'keen' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for avid that I've seen before include "Burning" , "Greedy - enthusiastic" , "Keen or greedy" , "passionate" , "Eager like diva" .)