Chief supplier to Spooner (6)
I believe the answer is:
leader
'chief' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for leader that I've seen before include "Chief or front man" , "Important (newspaper) article" , "important member of orchestra" , "Principal player in an orchestra" , "Guide; editorial" .)