Company man's influential (6)
I believe the answer is:
cogent
'influential' is the definition.
(thesaurus)
'company man's' is the wordplay.
'company' becomes 'co' (abbreviation).
'man' becomes 'gent' (gent is a kind of man**).
'co'+'gent'='COGENT'
(Other definitions for cogent that I've seen before include "Compelling (argument)" , "Strong" , "Convincing, persuasive" , "Compelling or convincing" , "Forceful and to the point" .)