Space:1999 - End of Eternity

While exploring an asteroid, the Alphans critically injure an alien trapped within. Bringing him to Alpha, he is declared dead. However, he recovers spontaneously and his wounds have completely healed. The indestructible Balor is a scientist whose people had discovered the secret of immortality. He explains that his people branded him a dissident as their society descended into malaise brought about by widespread deathlessness. He was imprisoned inside the asteroid and cast out. Actually Balor is a psychopath, offering a drastic solution to his people's apathy; now freed of the eternal prison, he plans to spend eternity practicing the art of pain and torture, with the Alphans as his subjects.