Rickman of "Galaxy Quest” (4)
I believe the answer is:
alan
'rickman of galaxy quest' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for alan that I've seen before include "English name" , "-- Sugar, British entrepreneur" , "-- Ayckbourn, English dramatist" , "Boy" , "- Bates, - Bennett" .)