The disappearance of the elderly Zefram Cochrane, who set out into space to die and was instead found and rejuvenated by the Companion on a planetoid in the Gamma Canaris region.
Zefram Cochrane, inventor of the warp drive, vanished about a hundred and fifty years before the original series episode Metamorphosis. Aged eighty-seven, he had left his home at Alpha Centauri in a small ship, wanting to die in space. He was presumed dead and his body was never recovered.
In 2267 the shuttlecraft Galileo, carrying Kirk, Spock, McCoy and the gravely ill Commissioner Nancy Hedford, is pulled down to a planetoid in the Gamma Canaris region. There they meet Cochrane, apparently a man in his thirties.
An energy being he calls the Companion had found his disabled ship, restored his youth and kept him alive ever since. When the Companion joins with the dying Hedford, Cochrane chooses to stay with her, and asks Kirk to tell no one that he was found.