During its aeons of operation, it was tasked with scanning the memories of the visitors who came to the planet for recreation. The planet's machinery would create the objects that the visitors desired. The Keeper oversaw operation of the planet for many years, but when the USS Enterprise visited in 2269, they discovered the caretaker was dead. It hoped to take control of the Enterprise, who it thought was the master of its crew.
After discussions with Uhura, James T. Kirk, and Spock, it decided to remain on the Amusement Planet, continuing its original task as a way to have the galaxy come to it instead of conquering it. It granted the Enterprise crew shore leave on the condition that they continued the conversation, a duty with which Spock was tasked. (TAS: "Once Upon a Planet")