The fourth film in the series, "Conquest of the Planet of the Apes" explains how apes usurped the Earth from humans and set the stage for the previous films. Following a pandemic which kills all cats and dogs, humans begin using apes as pets, servants, and eventually slaves. Armando (Ricardo Montelbán), a circus ringmaster appears with Milo (Roddy McDowell), his simian performer who hides his true identity as the son of two apes from the future. After viewing the cruel treatment of the apes in Central City, Milo runs and hides among the slaves; here, he becomes the property of Governor Breck (Don Murray) and is put to work by the kind Mr. MacDonald (Hari Rhodes). Under his newly-given name, "Caesar" conspires with his fellow apes, plotting his rebellion against the human overlords. Two-time "Planet of the Apes" veteran Natalie Trundy also reappears briefly as Lisa, the chimpanzee mate of Caesar.