The son of Mary Sue and L. Ron Hubbard, Quentin was frequently named as the successor to his father as the head of the Church of Scientology.

At the end of October of 1976, Quentin was found comatose in a parked car in Las Vegas with the engine still running. He was rushed to a hospital where he died two weeks later, without regaining consciousness. He was not identified until several days after his death. Although no precise cause of death was determined, he had certainly suffered from carbon monoxide poisoning. He was twenty-two years old.

Quentin had tried to measure up to his father's expectations--he was one of the few top grade Class Twelve Auditors--but he didn't share his father's temperament. He had pleaded with his father to let him leave the Sea Org. He had disappeared several times. There was also an aspect of his nature which couldn't be reconciled with his father's philosophy: Quentin was a homosexual. There's little doubt his death was suicide, he had attempted it before.