Frequent Poirot portrayer (7)
I believe the answer is:
ustinov
'frequent poirot portrayer' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ustinov that I've seen before include "Peter, film actor and director" , "Sir Peter --, raconteur" , "past actor" , "Peter __, actor, playwright and raconteur, d. 2004" , "British actor and playwright" .)