The Kell's Scourge is an anarchist Fallen terrorist syndicate led by Siviks, Lost to None with hideouts across the Solar System. They are hellbent on sowing chaos wherever they go and actively seek to use the technology of the Black Armory to gain power and control.
At some point before the campaign, Siviks fell out with his brother (The Spider) and was imprisoned in the Prison of Elders, only to escape and formed the Kell's Scourge as a rival syndicate from his brother's. Siviks and his crew uncovered the Gofannon Forge on Nessus, which they used to upgrade their weaponry with Black Armory technology and smuggle among the other malcontent Fallen that later joined their rebellious cause.
Forming holdouts all across the system, the Scourge began to plunder for more Black Armory tech and gained the support of deserting House of Dusk members, whilst making a push into the Spider's territory as his competition. This forces the Spider's hand to reach out to the Guardians and reveal the secret location of the Black Armory hidden within the Last City. With the reluctant support of Ada-1, Guardians began engaging with the Scourge at the EDZ and recovered the Volundr Forge from the Red Legion in the process.
Attempts at tracking Siviks and his Fallen caches across the European Dead Zone lead to a delivery note yielding the Scourge's base of operations on Nessus. There the Guardians disrupted an exchange between Siviks and Telksis, the Pillager, killing the latter and then securing the Gofannon Forge from Zevious-3, the Forge Warden.
Seeking to plunder the Black Armory Vault of its secrets, the Kell's Scourge unleashed its Prime Servitor, Insurrection Prime, to breach the Last City and allow the anarchist Fallen to occupy a desolate section of it. In retaliation, the Vanguard issued a six manned raid into Scourge territory and destroy the war machine at all costs. Insurrection Prime was destroyed, but not before Siviks stole pages from the logs of the Armory's founders; which the Guardian would reclaim from the Scourge.
In a final bout to get an edge, Siviks lead an assault upon the restricted Niobe Labs, attaining control over the security protocols which defended the lab and aiming to obtain the Obsidian Accelerator from the Bergusia Forge, thereby attaining blueprints for a mobile forge which would've heavily upgraded Fallen weapon and armory. Their victory was however short-lived as the arrival of The Guardian brought destruction upon the Scourge, causing Siviks to retreat and release The Black Recluse to protect the final forge, named precisely to mock the Spider, but is thwarted by the Guardians. In a final standoff Siviks, the Spider's mad brother, is put to an end, helping Ada-1 and the City and reclaim the Black Armory's secrets and technology whilst leaving the Kell's Scourge left leaderless and utterly crippled.
Following their crippled state, it appeared the Scourge's few remaining members splintered throughout the system, one such example being a Servitor belonging to the Scourge found in the K1 Communion Lost Sector. 
The Kell's Scourge is similar to that of the Spider's, with both groups being Fallen criminal organizations that are working for their own interests. They are also similar to the Devil Splicers, with both groups being bands of nefarious Fallen terrorists who harness Golden Age technology for their own purposes.
List of appearances