Fighter happy one by a hill (9)

I believe the answer is:

gladiator

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'fighter' is the definition.
(I know this)

'happy one by a hill' is the wordplay.
'happy one' becomes 'gladi' (I am not sure about this - if you are sure you should believe this answer much more).
'by' is a charade indicator (letters next to each other).
'hill' becomes 'tor' (tor is a kind of hill).
'gladi'+'a'+'tor'='GLADIATOR'

Can you help me to learn more?

(Other definitions for gladiator that I've seen before include "Roman arena fighter" , "Colosseum combatant" , "picture" , "Gold tiara (anag.)" , "Roman arena combatant" .)

I've seen this clue in The Sun.

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