The Darkness is an ancient and powerful entity and the sworn enemy of the Traveler. It had spent millennia chasing and trying to destroy it. When the Traveler came to Earth sparking an age in Human history known as the Golden Age where technology boomed and they terraformed planets and colonized the Sol System, soon after the Darkness loomed in on the Traveler, ending the age of prosperity the Traveler had brought and started a chain of events known as the Collapse.
Certain classes of the Hive, such as Wizards, are able to use the power of Darkness akin to how the Guardians are able to wield the power of the Traveler.  Other species are also linked to this omniscient force, such as the Cabal, Fallen and the Vex.
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