Solacris was a technical solution of the Asgard to act as part of their own caretaker species. However, it backfired when it resulted in crippling the Asgard race and creating a plague which killed all of the unascended Ancient. The Solacris were revealed to be the cause of the Alliance's dissolution (composed of Ancient, Asgard, Furling and Nox races).
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Interestingly, in some accounts, the Ori, who were a renegade faction of Ancients, were rumored to have remade the plague for their priests, the priors, to use on any unbelievers to enforce their belief, Origin.