Mr Harris's uncle (5)
I believe the answer is:
remus
I believe this clue is a double definition.
'mr' is the first definition.
'harris's uncle' is the second definition.
(Uncle Remus, Joel Chandler Harris character)
(Other definitions for remus that I've seen before include "twin brother" , "J. C. Harris's storyteller Uncle" , "partner in City foundation" , "murdered brother?" , "City founder - "uncle" storyteller" .)