Ever since Destiny launched back in 2014, fans have wondered what the Darkness actually is.
The Darkness is the Destiny universe’s overarching threat, a mysterious force opposed to the Light. The Light, which grants the Guardians their super powers and gives the Ghosts, the little floating robot things that work with the player throughout the game, life, originates from the Traveler. The Darkness, it seems, works in opposition to the Traveler, which made some grand last stand on earth as it fended off this threat years before the first game begins.
Destiny 2’s campaign suggested the Darkness was finally on the march via a post-credits scene which showed mysterious pyramid ships heading earth’s way. And then the Warmind DLC revealed the Worm gods, the scaly deity species which billions of years ago gave the Hive their power, commune with and are in turn sort-of disciples of the Darkness.
Source: Eurogamer Destiny fans reckon they've uncovered a description of what the Darkness actually is