Giant who mastered his associate? (5)

I believe the answer is:

magog

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

I can't explain the rest of the clue.

(Other definitions for magog that I've seen before include "Gog's companion" , "old giant" , "Biblical king" , "Gog and -, City of London guardian giants" , "Last of two old giants" .)

I've seen this clue in the Evening Standard.

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