Rat

"We wanted to cure cancer, Alzheimer's, and so
much more. Ethics demanded that we not use
humans, so we turned to rats. We cured
Alzheimer's in them, gave them better brains.
We made them disease resistant when attempting
to cure cancer in them. In our quest for medicine,
we made them more and more human. Then
one day we looked around our labs, and we
realized we were surrounded by hordes of hyper
intelligent, super powerful rats. And they were angry."
- Excerpt from the History