Kariel

Kariel was a female who was once a corporeal lifeform, but then merely reached a different state of existence. She was tall and slender, with long flowing hair of spun copper that seemed to float in slow motion. She also had abnormally large emerald green eyes, soft skin, a scent that smelled like roses, and gave off an aura of safety.

Kariel served as a guide to James T. Kirk after he died to help him in his next stage of development. But before that, she allowed him the chance to change something in his past life, like correcting a problem, or to go on his current course of existence unchanged. Kirk decided to go back in time and save the life of Edith Keeler. (SS TOS (Remembering the Future))