The Caretaker, also known as the Keeper, was a male from an advanced alien race. He was the last individual of his race residing on the Shore Leave Planet. This person was responsible for overseeing the proper operationn of the planet.
In 2267, crew from the USS Enterprise visited this planet, and after a series of unexplained occurrences, met this caretaker. He offered apologies for their confusion, explaining that he had not initially realized the planet's nature was unknown to the visitors. He described the planet as a place his people had constructed so they might play. He then offered the use of the planet for shore leave, as long as appropriate precautions were taken. But he would not comment on his people, saying enigmatically that the Federation visitors were not yet ready to understand them – a statement with which Spock concurred. (TOS: "Shore Leave")