Voids

Voids are a species formed from other species that were corrupted by the power of the Darkness. Voids are attracted by the Light's energetic output, which lead them to constantly being present at Io, Tangled Shore in the Asteroid Belt, Dreaming City in Jupiter, in Mars (only in the Exclusion Zone, attracted by the Dark Heart), and in the northern shores of the European Dead Zone, attracted by the Light emitted by the Traveler's Fragment from the Forbidden Forest. Voids spawn from Interdimensional Rifts and Void Gates.

Birth of the Darkness
Many mysteries surround this enigmatic population of vile, sightless creatures known as the Voids up to date. All that is known is that the Voids spawned in the Solar System through the Dark Garden when the Vex experimented the Heart's matter in other lifeforms, creating corrupted Void versions of the Fallen and the Hive, and these twisted specimens crawled out of the Exclusion Zone to swarm the system's planets, mainly those in which the Light was actively present, this corruption happened due to the fact these beings were exposed and imbued with the Darkness. Unlike the Light, that empowers its user, the Darkness corrupts the being it is present in and dominates its will to make him part of a bigger plan. After the destruction of the Dark Heart, the Voids escaped our dimensional plane through Interdimensional Rifts and Void Gates. They would later return through the same sources, this time even more empowered by the Darkness and given the abillity to corrupt other beings as stated by Asher Mir in his research for the Voids in Io, which was one of the places they were more active in a certain period of time.

Corruption of Vex and the Cabal
Given the abillity to corrupt other lifeforms - except for humans, Awoken, and Exo who possessed a connection to the Traveler's Light - the first victims of the Voids would be the Cabal, who drawn their attention when they entered the Solar System in mass armies at the order of their Emperror Ghaul.

The next step for the Voids would be to "recruit" the help of the species that were directly responsible for their creation, the Vex collective. Still in Io, as Ikora Rey and Asher Mir discovered with the help of the Guardian, the Voids were undergoing a process of mass corruption of the Vex collective, giving birth to new classes of Voids. The Voids' initial objective was to corrupt the entire collective, but as Asher Mir stated, "not even the Voids could dominate such a huge network that the Vex created".