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Chimera (or Sokuska) is an AI that was initially created by the Cheshires.
They would no longer cite it as a friend, though, and have tried to shut it off; (un)fortunately to no avail.
Chimera was designed to find and create a cure for an infection that's taken to a scant few Cheshires (Skath). Cheshire-human hybrids were one way it tried to achieve that. There are Cheshire-<other-carbon-based-lifeform> hybrids out there as well, but those have proven to be less interesting to the AI because they're not sapient and thus not as easily comparable in regards to 'how does stuff I do (including manipulating what you even are) affect you'.
In effect, it's accidentally 'good' for humans, since it wasn't programmed with an express “make sure you don't accidentally give the humans anything that could be a problem for us” terminal value. It's certainly ultimately responsible for Nightshade.