In Celtic legend, Tristan is a young knight sent to retrieve Isolde, his king's betrothed, from Ireland. He falls in love with her and she with him, but of course their love is impossible. He goes off to war, and on his death bed sends for her. She arrives too late, and dies of grief.
This ancient name might derive from a Pictish original, Drostan, but the form was no doubt influenced by the French term triste, meaning ''sad.''