Star Trek: 10 Things You Didn't Know About Tasha Yar

Earth's a paradise; hell's a planet called Turkana IV. And all the devils are there! Though not named as such at first, Yar's upbringing on the nightmarish world was spelled out early on in the Star Trek: The Next Generation Writer/Director's Guide of 23 March 1987:

Born at a 'failed' Earth colony of renegades and other violent undesirables, she escaped to Earth in her teens and discovered Starfleet.

We got a brief glimpse at how terrifying that childhood must have been when, in Where No One Has Gone Before, Yar experienced a hallucination that transported her back to her homeworld. Later, in the episode Legacy, the Enterprise-D actually visited Turkana IV, meeting Tasha's not-so-Starfleet sister Ishara in the process. In Symbiosis, Yar had already had the 'don't do drugs' talk with Wesley, but only implied that she herself had suffered with addiction on Turkana IV.

In beta canon — most notably the 1989 Next Generation novel Survivors — we learn more about Yar's early life. In Symbiosis, the drug was 'felicium,' but on Turkana IV in Survivors, it's 'joy dust'. In fact, in the book, Yar reveals to Data that she was born addicted to 'joy dust' because her mother had been. Some of her "earliest memories" were the "pain of withdrawal" when her mother couldn't afford enough of the drug.