Swarm was one of the two Ravagers who led the fight against the Time Lords in the Founding Conflict which ended the Dark Times, opposing the Time Lords' intention of using the power of the Mouri to bind time. Defeated at the Siege of Atropos by the Fugitive Doctor, he was subsequently imprisoned in a containment chamber at the Burnished Rage battleground by the Division. After freeing himself in a new incarnation, he revealed to the amnesiac Thirteenth Doctor that he had been the Fugitive Doctor's archenemy in their life as a Division agent, and attempted to harm the Mouri once more following the Flux, allowing the Time Force to be unleashed.
He had the ability to burn living things to ash with a single touch, to teleport himself across space and time at will, and even to drain away life from his enemies to fuel a regeneration.
He noted that "Swarm" and "Azure" was not his and his sister's actual names but merely translations, albeit serviceable ones.
Incarnations of Swarm
At some point, the Old Swarm and Azure took over the Temple of Atropos on the planet of Time, holding numerous hostages within Passenger forms. A team of Division agents led by the Fugitive Doctor captured them with the aid of the Mouri. (TV: Once, Upon Time) The Mouri were subsequently quantum-locked against them in fear of their return. (TV: War of the Sontarans)
Swarm was imprisoned in a containment chamber, allegedly at "the dawn of the universe". Every thousand years, agents of the Division would come check whether he was still secure in his containment. During what would become En Sentac's last such tour, Swarm managed to disable all the technology keeping him frozen. Using his psychic powers to freeze En Sentac in place, Swarm kept her paralysed for a few moments before draining her life force and renewed himself into a new form. (TV: The Halloween Apocalypse)