"The fellow in the white hat", I put in, "is the boss" (5)
I believe the answer is:
chief
'the boss' is the definition.
('chief' can be a synonym of 'boss')
'the fellow in the white hat i put in' is the wordplay.
'the fellow in the white hat' becomes 'chef' (I can't explain this - if you can you should give a lot more credence to this answer).
'put in' indicates putting letters inside.
'chef' enclosing 'i' is 'CHIEF'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for chief that I've seen before include "Head of a native American tribe" , "Person in charge, head" , "Tribal head" , "Organisation head" , "Ordinary type" .)