Shmi Skywalker is a human female, enslaved in Mos Espa on Tatooine and the mother of Anakin Skywalker. The StarWars.com Databank records that she raised him alone until Qui-Gon Jinn recognised his Force sensitivity and secured his freedom for Jedi training, and that she was later bought and freed by the moisture farmer Cliegg Lars, whom she married. She was introduced in Star Wars: Episode I The Phantom Menace (1999), played by Pernilla August.
The one who is left behind
Qui-Gon wins Anakin's freedom in a bet and cannot win hers. That detail — a Jedi negotiating for one person and walking away from the other — is the first thing the prequel trilogy says about the Order, and it is far more damning than anything the Council does later.
Her death is the engine
The Databank is direct: "Tusken Raiders captured Shmi and tortured her," and Anakin arrived too late. The massacre that follows is the first unambiguous atrocity he commits, and the film ties it explicitly to his resolve to become powerful enough to stop people dying. Everything from Mustafar to the Death Star runs back through a farmhouse outside Anchorhead.
What she is not
She is not given a Legends counterpart of any weight, she is not given a homeworld other than the one she is enslaved on, and no verifiable line of hers survives in the transcripts consulted for this entry — so this dossier carries no quotes. The saga's origin point is a person the saga barely lets speak, and pretending otherwise with an invented line would make that worse, not better.
Where to read her
The Phantom Menace novelisation by Terry Brooks opens with material on Anakin's childhood that the film compresses, and the Attack of the Clones novelisation covers the Lars homestead and her final days.