SIVA

"We thought we were indestructible, the Lords of Iron. We swore we would do anything to protect the Last City. Some of us paid the ultimate price. I am all that remains. We thought we had sealed away the plague for eternity, but now it has returned, and this time with a Fallen army. It is time to avenge my fallen brothers and sisters. Stand with me, Guardian. Prove yourself worthy, and the Iron Lords will rise again!"

- Saladin Forge

The SIVA plague was once a Golden Age breakthrough in self-assembling, self-replicating nanotechnology. It was discovered by the Iron Lords during the early city age, and turned against them in their attempt to utilize it for humanity's betterment. Unable to destroy the techno-virus, the Iron Lords sealed it beneath the earth, deep within the bowels of the Cosmodrome.

A year after the Taken War, while looting ancient tombs from the Golden Age, the Fallen House of Devils managed to unearth SIVA once more. Realizing the potential of this nanotechnology, their Splicers harnessed and began infecting their fellow Devils, in an attempt to turn them into machine gods. Unable to defeat the mutated Devils on his own, Saladin began seeking out Guardians to help him form a new generation of the Iron Lords to defeat the mutant army and end the threat of SIVA once and for all.

Trivia
SIVA is also known as Ironsbane, presumably for wiping out the Iron Lords.