Natasha "Tasha" Yar was a human female introduced in the Star Trek: The Next Generation pilot Encounter at Farpoint.
She was portrayed by Denise Crosby, who had also portrayed Sela.
History
Tasha was born on the failed human colony of Turkana IV in 2337 as the government of the colony collapsed and street gangs took over. She was born addicted to joy dust due to her mother having taken it during pregnancy. Tasha's earliest memories were of withdrawl pains when her mother no longer gave her joy dust.
Tasha's sister Ishara was born in 2342. Soon aftewards her parents had either abandoned the pair altogther or had died. Tasha and her sister were taken in by a woman named Yar until Yar's 2349 death. Soon afterwards Yar's death Tasha was gang raped by one of the colony's many gangs. Tasha then learned to defend herself and in the subsequent years killed two men who tried to rape her.
She was rescued by the crew of the USS Cochrane in 2352. Tasha tried to get Ishara to come with her, but Ishara refused to come along. Taken to Earth Yar underwent counseling and remedial education. A couple years later she was accepted into Starfleet academy, and graduated with honors in 2359.
By 2363 Yar was serving as assistant security chief on the USS Victory when the ship responded to a distress call from Kirishia. She entered a Carnellian minefield in order to reach a wounded colonist. Seeing her bravery, Captain Jean-Luc Picard asked that she be assigned to the Enterprise-D.
The following year Yar was assigned to the Enterprise-D as security chief under Captain Picard. She piloted Picard to the ship for the ceremony in which Picard officially took command. Soon after the Enterprise left Earth and the crew had their first run in with Q. After being provoked by Q, the powerful entity briefly froze her in response.
Yar remained as security chief through 2364. She became close to the senior staff, especially Lt. Commander Data.
On stardate 41601.3 Yar was attacked by the malevolent being Armus and died a short time later due to synaptic failure. Her friend and colleague Worf succeeded her as chief of security.