It's what he has that makes him what he is (5)

I believe the answer is:

owner

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'he has that makes him what he is' is the definition.
'owner' can be an answer for 'he has' (I've seen this before). I'm unsure of the remainder of the definition.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for owner that I've seen before include "Person having property" , "Legal possessor" , "The person in lawful possession" , "One who has something" , "One that secured" .)

I've seen this clue in the Evening Standard.

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