Crossword Genius

Terribly valiant, he becomes a monster (9)

Ross

I believe the answer is:

leviathan

'a monster' is the definition.
(I know that leviathan is a type of mythical creature)

'terribly valiant he' is the wordplay.
'terribly' indicates an anagram.
'valiant'+'he'='valianthe'
'valianthe' is an anagram of 'LEVIATHAN'.

'becomes' acts as a link.

(Other definitions for leviathan that I've seen before include "Huge (sea) monster" , "An evil hat turns to anything of great size" , "Monstrous sea creature" , "Biblical sea-monster" , "Monstrous beast" .)

I've seen this clue in The Daily Express.
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