Though the Caretaker is not humanoid, it uses a holographic human avatar when communicating with the Voyager crew. This avatar was portrayed by the late Basil Langton.
The Caretaker assumed responsibility for protecting the Ocampa after his people inadvertantly destroyed the ecosystem of their home planet, halting all nucleogenic activity in the atmosphere and stopping it from producing rain. For over 1500 years, he protected the Ocampan race by building an underground city for them with access to a subterranean water supply, providing them power from his Array and defending them from the aggressive Kazon. However, the Caretaker did not realize that his actions were also rendering the Ocampa utterly dependent on his assistance. Suspiria, his mate, did realize this, and left him, taking a small group of Ocampa with her.
Some time before 2371, the Caretaker realized that he was nearing the end of his life and began seeking out compatible biological lifeforms with which he could procreate with in hopes of siring a replacement to carry on his work. He abducted starships from all over the galaxy, bringing them to his Array and analyzing the lifeforms from these ships, seeking compatible subjects to breed with. Very few subjects showed promise and even these few would all die after the Caretaker's tests afflicted them with some form of illness. As such, these sickly individuals were sent to live out the rest of their days with the Ocampa.
The Caretaker's search for a mate would come to an unsuccessful end in 2371 after he abducted the USS Voyager and the Maquis raider Val Jean from the Bajoran Badlands in the Alpha Quadrant.
Shortly after abducting Voyager, and recognizing that his death was imminent, the Caretaker began sending an increased store of energy to the Ocampa reserves, so that they would have enough to last up to five years after his death. However, when confronted by Captain Kathryn Janeway of Voyager, he began to realize that caring for them was not helping them, but making them dependent on him. Captain Janeway made him realize that the "children" (as he considered the Ocampa) had to eventually grow up. To help the Ocampa along, he sent them a record of his knowledge that would hopefully allow them to develop self-sufficiency.
A short time later, before he could send Voyager or the Val Jean back, the Caretaker died, leaving the two ships stranded over seventy thousand light years from home. Before he did so, he requested to Captain Janeway that the Kazon should not be allowed to use his array, forcing the Starfleet captain to destroy it.