Representative of a fellow (5)
I believe the answer is:
agent
'representative' is the definition.
(agent is a kind of representative)
'a fellow' is the wordplay.
'fellow' becomes 'gent' (synonyms).
'a'+'gent'='AGENT'
'of' is the link.
(Other definitions for agent that I've seen before include "Representative - means" , "He or she acts for actors" , "Catalyst" , "Middleman" , "Person who does business on behalf of another" .)