Tony goes mad about company magnate (6)
I believe the answer is:
tycoon
'magnate' is the definition.
(I've seen this before)
'tony goes mad about company' is the wordplay.
'goes mad' indicates an anagram.
'about' is an insertion indicator.
'company' becomes 'co' (abbreviation).
'tony' anagrammed gives 'tyon'.
'tyon' placed around 'co' is 'TYCOON'.
(Other definitions for tycoon that I've seen before include "Big noise" , "Rich businessperson" , "Big businessman" , "Magnate, wealthy businessman" , "Not coy? (anag)" .)