Legendary giant mastered by his partner (3)

I believe the answer is:

gog

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

'legendary giant' is the definition.
'gog' can be an answer for 'giant' (I've seen this in other clues). I am not certain of the 'legendary' bit.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Another definition for gog that I've seen is " Giant".)

I've seen this clue in the Evening Standard.

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