Lady Bonkers.
Lady Bonkers was one of the reasons that Peanuts/Simon put into play his master plan to free himself from the Boulle Behavioral Laboratory. She was one of the female chimpanzees at the Laboratory and despite the male and female chimps being kept separately there, Peanuts/Simon was nonetheless very attached to her. So Dr. Hasslip sent her to the Washington D.C. zoo.
After enacting his complex plan, Peanuts/Simon ended up at the zoo with Lady Bonkers.