Maniac Monkeys

"Monkeys, apes, they all hold stuff with their feet, man! We're talking freaks of nature!"

- Ron Stoppable "There once was a man who's prison was a chair. The man had a monkey, they made the strangest pair. The man was the prisoner, the monkey held the key. No matter how he tried, the man couldn't flee. Locked in his prison, terrified and frail. The monkey gaining power, keeping him in jail. The man tried to keep the monkey from his brain, but every move he made, he made the monkey's game. The monkey ruled the man, it climbed inside his head. And now as fate would have it, one of them is dead."

- Narrator for a commercial for Monkey Shines

These monkeys are used as signs that something bad is about to go down. Because of their similarities to humans, a superintelligent ape is going to suffer from an inherent sibling rivalry with the human race, and want to either wipe it out or subdue it. Often, in a series which features anthropomorphic animals, apes and monkeys will play the bad guys.

This trope is distinct from Killer Space Monkey in that these monkeys are usually Super Intelligent Mad Scientists who want to Take Over the World or at least make life difficult for humanity. Another possibility is that they are Genius Bruisers determined to both overpower and Out Gambit their fellow primates.

This here is the opposite of Everything's Better with Monkeys. Killer Gorilla is a subtrope, where the primate in question is not just malicious but also big and strong.