Irish princess and skillful healer. Her fiancee, Lord Morold is killed by Tristan. As Tristan comes to her, to be cured from a serious wound, she fails to revenge Morold because she falls in love with him. Later Tristan returns, to obtain her as a bride for King Mark. Hurt to the core of her soul she wishes death for herself and Tristan. Brangäne exchanges the death potion with the love potion and Isolde and Tristan continue to live. They commit treason to King Mark and after their love is unveiled, Tristan heavily wounded escapes to Karéol. Isolde follows and Tristan dies in her arms. Isolde goes with Tristan and her body drops down inanimately.
Tristan says, "She could soon cure my sickness just by calling me her love" (18.159).
After King Mark learns of the secret love affair between Tristan and Iseult, he banishes Tristan to Brittany, never to return to Cornwall. There, Tristan is placed in the care of Hoel of Brittany after receiving a wound. He meets and marries Hoel's daughter, Iseult Blanchmains (Iseult "of the White Hands"), because she shares the name of his former lover. They never consummate the marriage because of Tristan's love for Iseult of Ireland.
During one adventure in Brittany, Tristan suffers a poisoned wound that only Iseult of Ireland, the world's most skilled physician, can cure. He sends a ship for her, asking that its crew fly white sails on the return if Iseult is aboard, and black if she is not. Iseult agrees to go, and the ship races home, white sails high. However, Tristan is too weak to look out his window to see the signal, so he asks his wife to check for him. In a moment of jealousy, Iseult of the White Hands tells him the sails are black, and Tristan expires immediately of despair. When the Irish Iseult arrives to find her lover dead, grief overcomes her, and she passes away at his side.
This death sequence does not appear in the Prose Tristan. In fact, while Iseult of the White Hands figures into some of the new episodes, she is never mentioned again after Tristan returns to Cornwall, although her brother Kahedin remains a prominent character. The plot element of the fatal misunderstanding of the white and black sails is similar to—and might have been derived from—the story of Aegeus and Theseus in Greek mythology.
Sources: