In the Planet of the Apes movie series, Dr. Milo is a genius chimpanzee scientist, and a renegade who spurns the intellectual and technological limits placed on the ape society. He was portrayed in Escape from the Planet of the Apes by actor Sal Mineo, in one of his last roles.
Not a character from the original novel or movie, Dr. Milo was added to the storyline developed in Beneath the Planet of the Apes, in the interstitial period between Beneath and Escape. Whether Milo was an outcast from Ape City, or self-exiled from it, is not known. Unafraid of "the beast Man" and of human technology (forbidden under Ape law) as he is of reading banned books or visiting the Forbidden Zone, he is a friend of Cornelius and Zira, who also hold liberal views.
In the Forbidden Zone, Dr. Milo is able to raise the Icarus, the spacecraft that carried the astronaut Taylor but crash-landed in a lake, and is able to repair it well enough to relaunch. (It is never revealed how he learned of the ship, possibly in a conversation with Zira and Cornelius, or of electronics or any other technique used in space flight; his advanced intelligence would have provided some insight, possibly augmented by caches of old human books, or technological data found aboard the craft.)
While Milo never completely fathoms the technology or the purpose of the Icarus (and of course its crew are unavailable), he does come far enough to be able to attempt a flight. Cornelius and Zira join him, the three donning spacesuits and climbing aboard, after they become convinced the latest anti-human campaign will spell disaster. Once in space, they learn how true this becomes, as the Earth is destroyed.
Whether the Icarus followed a preprogrammed flight path, was affected by shock waves from the blast that destroyed Earth, or was flown by Dr. Milo is never revealed, as is whether the apes used the hibernation facilities aboard the ship. (From the attitudes shown in Escape, it is probable the apes knew very little about flying the ship, and simply let it follow its programming.) In any case, their trip takes the apes back in time to the year 1973, only months after the Icarus originally departed, and makes another water landing, this time floating off the California coast.
Startling their human finders, Dr. Milo, Zira and Cornelius are taken to the local zoo while the US Government ponders what to do with them. Finding themselves in the reverse situation of what astronauts Taylor and Brent went through coming to their world, the three chimpanzees agree to make no sounds around humans, but talk furtively in private, and try to decide how to handle what has happened. (Zira spoils this by openly declaring her dislike of bananas when the apes are fed, heightening the tension.)
As Dr. Milo paces, he draws the attention of a primitive gorilla from the next cage over, who grabs Dr. Milo at a vulnerable moment and strangles him to death. Mournful over the loss, Cornelius and Zira name their son (born toward the end of Escape) Milo, after their friend. To hide his identity, Milo's foster father Armando gives him the name Caesar. Caesar becomes the main character in the next two Apes movies, and the leader of a new ape society.