National leader — complete gonzo! (6)
I believe the answer is:
nutter
'gonzo' is the definition.
(both can mean crazy)
'national leader complete' is the wordplay.
'leader' says to take the initial letters.
'complete' becomes 'utter' (I've seen this before).
The initial letter of 'national' is 'n'.
'n'+'utter'='NUTTER'
(Other definitions for nutter that I've seen before include "loony" , "In slang, a crazy or eccentric person" , "Very eccentric type" , "Madman" , "fruitcake" .)