Sela

Sela is a Romulan commander, the daughter of a Romulan general and an alternate-timeline Tasha Yar, who was captured after travelling back aboard the Enterprise-C. In The Next Generation's "Redemption" she secretly arms the Duras family during the Klingon civil war. She later attempts to brainwash Geordi La Forge into an assassin in "The Mind's Eye" and, in "Unification", plots a Romulan invasion of Vulcan, thwarted by Picard and Spock.