He has to be what he is (5)
I believe the answer is:
owner
'he has' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for owner that I've seen before include "Title holder?" , "Holder, possessor" , "possessive type" , "Person having property" , "Person with legal title to something" .)