I honestly don't think the darkness is just one person or thing it's the essence of whoever is trying to destroy the universe for personal gain. Like the worms pushing oryx to clean the universe and create the perfect shape. Or the vex trying to sew themselves into the fabric of space and time and become universal law. I think it's just a dull personification of the evil that plagues the universe no matter who the host of destruction is.
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The darkness is a being but it Is also a place called the deep. The worm gods flow the deep. Like the traveler flows through the sky.