Sub-Commander Selok was an officer in the Romulan military, who served the Romulan Star Empire as a spy. She entered the United Federation of Planets posing as the Vulcan Ambassador T'Pel. By 2367, she managed to establish an honored name in her service.
When her espionage service was concluded, the Romulans arranged her accidental "death" while being transported from USS Enterprise-D to the D'deridex-class IRW Devoras so that she could return to the Romulan fleet. While the ruse was discovered and the espionage acknowledged, it was the Romulans that largely came out on top that day.(TNG: "Data's Day")