Originally surface dwellers and the dominant species of their homeworld, the Ocampans exhibited phenomenal mental powers far in excess of any similar race in Star Trek canon. Their amazing mental abilities were offset, however, by their extremely short 9-year lifespan.
The development of the Ocampan race was interrupted when an exploratory vessel from another galaxy chose to visit the Ocampan homeworld. The propulsion system of the intergalactic vessel caused an irreparable chain reaction in the atmosphere of the planet destroying the ability of the atmosphere to carry on a rain-cycle. According to Captain Katherine Janeway, the planet's atmosphere was "completely devoid of neucleogenics." The intergalactic explorers upon realizing their mistake, took upon themselves the responsibility of taking care of the Ocampans. The Caretakers built a massive underground cavern with access to the only remaining natural water source on the planet, and supplied it with energy via transmissions from a gigantic orbiting station. From this station, the "Caretaker" dutifully watched over the Ocampans, supplying every need and protecting them from every danger. As a result of this life of absolute ease, the Ocampans eventually stopped using their mental powers and due largely to their short lifespans, eventually forgot about them completely. Over time, the Ocampans became completely dependent upon the Caretakers for all necessities of life.
The Ocampans remained in this state until the only Caretaker remaining on the station began to die. This Caretaker reasoned that only his own offspring would be able to carry on his work of protecting the Ocampans, and so began a galaxy-wide search to find a genetically compatible race through which it might produce offspring. This search consisted of a long series of trans-galactic ship-jackings, which is how the Federation Starship Voyager came to be in the Delta Quadrant.
During the time of the Caretaker, the planet's deserted surface was inhabited by a subset of the Kazon race.