Denise Michelle Crosby is an English actress who portrayed Mary in AMC's The Walking Dead. She is an American actress best known for portraying Security Chief Tasha Yar in Season One of Star Trek: The Next Generation as well as Yar's own daughter, the half-Romulan Commander Sela, in subsequent seasons. She is also known for her numerous film and television roles and for starring in and producing the film Trekkies. She is the granddaughter of entertainer Bing Crosby.