Theatre company set up by one-time actor (9)
I believe the answer is:
performer
'actor' is the definition.
(thesaurus)
'theatre company set up by one-time' is the wordplay.
'theatre company' becomes 'rep' (short for 'repertory theatre').
'set up' is a reversal indicator.
'by' means one lot of letters go next to another.
'one-time' becomes 'former' (I've seen this before).
'rep' reversed gives 'per'.
'per'+'former'='PERFORMER'
(Other definitions for performer that I've seen before include "star?" , "Eg 9 [ACTRESS]" , "Fred Astaire, say" , "Thespian" , "Entertainer" .)