Terrible Tim trains road runner (13)
I believe the answer is:
administrator
'runner' is the definition.
(someone who runs things)
'terrible tim trains road' is the wordplay.
'terrible' indicates an anagram.
'tim'+'trains'+'road'='timtrainsroad'
'timtrainsroad' anagrammed gives 'ADMINISTRATOR'.
(Other definitions for administrator that I've seen before include "Business organiser" , "One managing business affairs" , "One who manages or directs" , "Official organiser" , "Manager, controller" .)