Around the year 2065, the SS Valiant was swept into the galactic barrier and exposed to strange energies. Six of the crew were killed, and one developed psychokinetic abilities. Shortly afterwards, the ship's captain ordered its destruction.
In 2265, the USS Enterprise discovered the Valiant's disaster recorder. Retracing the Valiant's course, the Enterprise also encountered the barrier and was overwhelmed with strange energy. Nine crew members, all with high-level esper ratings, were killed; Lieutenant Commander Gary Mitchell and Doctor Elizabeth Dehner were also struck by the energy. The first effect on Mitchell was a reflective silver color in his eyes. Later, he began to develop mental and psychic abilities, including extrasensory perception, telepathy, and telekinesis. Dr. Dehner gained the same abilities slightly later. Mitchell also underwent personality changes, causing him to become a threat to the Enterprise and his crew-mates. Dehner eventually assisted Captain James T. Kirk in killing Mitchell, at the cost of her own life. (TOS: "Where No Man Has Gone Before")
In 2381, during a second contact mission to Apergos, Ensign Beckett Mariner power-washed a building, exposing a mechanism which reacted to the light of the planet's sun and began emitting strange energies. Commander Jack Ransom was struck by the energy and knocked unconscious. When he awakened shortly thereafter, he began to hover in the air. Ransom healed his own injuries and repaired his torn uniform. He was able to read minds, move objects with his mind, emit multicolored light from his hands, and physically alter people and objects. He was even able to separate his head from his body, cause it to grow to giant size, and move it into orbit, while his body remained on the planet below. After Ransom threatened to eat the Cerritos, Mariner weakened him by kicking his body in the genitals, and Dr. T'Ana disabled him by dropping a boulder on him. She was subsequently able to return him to normal. Ransom retained no memory of his actions while fully enpowered, saying that he had turned into "a monster". (LD: "Strange Energies")