In the Old Testament, son of Isaac and Rebecca and twin brother of Jacob, to whom he sold his birthright (4)

I believe the answer is:

esau

(Other definitions for esau that I've seen before include "Would-be fratricide" , "Isaac's hairy son" , "Jacob's brother (Gen.)" , "Biblical brother to Jacob" , "Jacob's brother (OT)" .)

I've seen this clue in The Independent.

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