Fellow captures a being from another plant (7)
I believe the answer is:
martian
'being from another plant' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'fellow captures a' is the wordplay.
'fellow captures' becomes 'marti' (I can't justify this - if you can you should believe this answer much more).
'a' becomes 'an'.
'marti'+'an'='MARTIAN'
Can you help me to learn more?
(Other definitions for martian that I've seen before include "One living on red planet" , "Sci-fi character" , "Being from another planet" , "Relating to one planet" , "Sci-fi alien" .)