Iseult (also Isolde) was a princess in medieval Arthurian legend; known as Iseult the Fair. She was the daughter of King Anguish of Ireland. Tristan was sent to seek her hand on behalf of his uncle, King Mark of Cornwall.
Iseult is first met as the lady who helps heal Tristan, under a false name, after his battle with Morholt. When Tristram's identity is revealed, he flees back to his own lad. Later, Tristan returns to escort Princess Iseult to Cornwall to marry King Mark. En route back to Cornwall Tristan and Iseult mistakenly drank the love potion intended for the wedding night of Iseult and Mark and fell hopelessly in love.
Iseult was bound to marry King Mark, but she and Tristan continued their affair until Mark became suspicious and Tristan had to flee. Additional episodes are integrated into the narrative as well, including several involving the great Saracen knight Palamedes' unrequited love for Iseult, In the Prose Tristan, the lovers' end comes when Mark finds them as Tristan plays the harp for Iseult beneath a tree. The cruel king stabs his nephew in the back, and Tristan, at Iseult's request, fatally crushes his beloved in a tight embrace as his final act.
The tragic story is part of the body of Arthurian literature. Versions of the legend were told by Thomas of Brittany (fl. 12th century), Gottfried von Strassburg (fl. 12th-13th century), Alfred, Lord Tennyson, and Richard Wagner.