Bird with old revolutionary (4)
I believe the answer is:
tito
'revolutionary' is the definition.
(I've seen this before)
'bird with old' is the wordplay.
'bird' becomes 'tit' (tit is a kind of bird).
'with' says to put letters next to each other.
'old' becomes 'o' (abbreviation).
'tit'+'o'='TITO'
(Other definitions for tito that I've seen before include "Yugoslavian freedom fighter and president" , "Former leader of country" , "Yugoslav marshall, prime minister and president, d. 1980" , "President of Yugoslavia, 1953-80" , "Head of state" .)