“The greatest” so-called country without leader (3)
I believe the answer is:
ali
'the greatest so-called' is the definition.
(Muhammad Ali was known as the Greatest)
'country without leader' is the wordplay.
'country' becomes 'Mali' (Mali is an example).
'without leader' means to remove the first letter.
'mali' with its initial letter taken off is 'ALI'.
(Other definitions for ali that I've seen before include "Son-in-law to Muhammad" , "Champion boxer" , "Muhammad ___ (or MacGraw?)" , "Champion of ring" , "Ringmaster" .)