Being valiant, he freed monstrous beast (9)

I believe the answer is:

leviathan

I'm a little stuck... Click here to teach me more about this clue!

'monstrous beast' is the definition.
(I've seen this before)

'being valiant he freed' is the wordplay.
'valiant he' can be anagrammed to 'LEVIATHAN'.
Though, I am not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for leviathan that I've seen before include "Autocratic monarch" , "Gigantic" , "Monstrous beast" , "Huge (sea) monster" , "Monstrous sea creature" .)

I've seen this clue in The Irish Times.

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