Guinness of films (4)
I believe the answer is:
alec
'guinness of films' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for alec that I've seen before include "Sir - Douglas-Home, former PM" , "Guinness (a smart lad?)" , "Smart man?" , "Actor Guinness is smart" , "Smart ..., he thinks he knows everything" .)