Lieutenant Tasha Yar (Denise Crosby) was killed off before the end of Star Trek: The Next Generation season 1, but she made a strange comeback later on in the series. Created by Gene Roddenberry, TNG was the first spinoff of the classic Star Trek: The Original Series. Premiering in 1987 and starring Patrick Stewart as Jean-Luc Picard, the Captain of the U.S.S. Enterprise-D, TNG ran for seven highly successful seasons and spawned four TNG movies. But by Denise Crosby's own choice, Tasha Yar missed almost all of TNG's triumphs.
Denise Crosby was a series regular on Star Trek: The Next Generation season 1. Lt. Natasha Yar was the Enterprise's Security Chief, an impressive accomplishment for a Starfleet Officer who was only 27-years-old. Tasha was highly respected among the crew, formed a friendship with Counselor Deanna Troi (Marina Sirtis), and, despite being an android, Lieutenant Commander Data (Brent Spiner) developed an intimate relationship with Yar, which was a crucial, early step in his quest to become more human. Tasha earned the Klingon Lieutenant Worf's (Michael Dorn) admiration for her fighting abilities and Yar also regarded Captain Picard as a mentor. In her role as Security Chief, Tasha regularly accompanied the Enterprise's First Officer, Commander Will Riker (Jonathan Frakes), on Away missions. But it was during an Away mission to Vagra II in "Skin of Evil", the 23rd episode of TNG season 1, that Tasha was unceremoniously murdered by an alien creature called Armus. With her sudden death, Tasha Yar became the first Star Trek series regular to be killed off and Worf took her place as Security Chief.
As Crosby told TrekMovie in a 2012 interview, she asked to leave TNG because she was "miserable" and she "couldn't wait to get off that show". TNG season 1 experienced a number of growing pains behind the scenes, including a large amount of turnover in its writing staff due to the intense pressure of living up to the success of the original Star Trek. But for Crosby, playing Tasha Yar quickly grew monotonous. The actress explained:
I didn’t want to spend the next six years going “Aye, aye, captain,” and standing there, in the same uniform, in the same position on the bridge. It just scared the hell out of me that this was what I was going to be doing for the next X-amount of years.
Crosby's exit from TNG was amiable and she received Gene Roddenberry's blessing to pursue her career goals elsewhere. But that wasn't the end of Tasha Yar's story because, to Crosby's surprise, the actress was asked to reprise her role just two years later. In the TNG season 3 episode "Yesterday's Enterprise", the arrival of the U.S.S. Enterprise-C through a temporal rift created an alternate timeline that placed Tasha Yar back on the Enterprise's bridge in a new reality where she never died and the United Federation of Planets was at war with the Klingons. After Guinan (Whoopi Goldberg) convinced Yar and Picard that this reality wasn't meant to be, Tasha chose to accompany her new love interest, Lieutenant Richard Castillo (Christopher McDonald), back to the Enterprise-C to die with him in the past and set the timeline back to normal.
But the alternate Tasha's story didn't end there and got even stranger. Yar didn't die but she was captured and enslaved by the Romulans. She then gave birth to a half-Romulan daughter named Sela, who was played by Crosby as an adult, making Denise the first Star Trek actress to portray her own offspring. In fact, Crosby created the idea of Tasha having a daughter, who TNG's writing staff revised to be half-Romulan. After her mother was executed when she was 4, Sela grew up to become a Romulan Commander who was an enemy of the Enterprise-D. Sela clashed with Picard's crew in the "Redemption" and "Unification" two-parters but her final fate was never defined.
Finally, the original Tasha Yar reappeared in the TNG series finale, "All Good Things", which was set in three different time periods of Picard's life. In the past events occurring during the events of Star Trek: The Next Generation's series premiere, "Encounter at Farpoint", the young Tasha was once again at her station as Security Chief of the U.S.S. Enterprise-D.