Richard Castillo

Richard Castillo was a Starfleet officer. He was first assigned as a cadet to the USS Enterprise-C in 2332, where he took a position as helmsman after the death of the ship’s original helmsman. (anthology Enterprise Logs: "Hour of Fire") He remained on the vessel for 12 years, eventually reaching the rank of Lieutenant. In 2344, Enterprise was caught in a battle with the Romulans, and was sucked into a temporal vortex. He met Natasha Yar in the future, and began a relationship with her. He and Yar took Enterprise back into the past, where Enterprise was destroyed. ("Yesterday's Enterprise") Castillo was killed by a Romulan commander for insolence shortly after being taken captive. (TOS novel: Vulcan's Heart)

Note: A short story in Strange New Worlds tells of a different fate for Castillo, somehow having escaped the Romulans and survived to at least the time of Star Trek: The Next Generation.