Tissaia de Vries is one of the most respected mages on the Continent and the rectoress of Aretuza, the school for sorceresses on the island of Thanedd. She is strict, dignified and deeply committed to the idea that magic carries responsibility. She is also a member of the Council of Wizards, which makes her one of the people who help decide the fate of the North.

Her importance to the saga comes largely through Yennefer, whom she took in as a student and trained. Their relationship is complicated, a mix of discipline, pride and unspoken care. Tissaia is also present at the gathering on Thanedd, the political summit that turns violent and marks a turning point in the story.