(Middle Ages) the nephew of the king of Cornwall who (according to legend) fell in love with his uncle's bride (Iseult) after they mistakenly drank a love potion that left them eternally in love with each other

Tristan (Latin/Brythonic: Drustanus; Welsh: Drystan; Portuguese: Tristão; Spanish: Tristán; also known as Tristran, Tristram, etc.) is one of the main characters of the Tristan and Iseult story, a Cornish hero and one of the Knights of the Round Table featuring in the Matter of Britain. He is the son of Blancheflor and Rivalen (in later versions Isabelle and Meliodas), and the nephew of King Mark of Cornwall, sent to fetch Iseult back from Ireland to wed the king. However, he and Iseult accidentally consume a love potion while en route and fall helplessly in love.

a bit more of poacher than Kluivert though