Tristram was a mythical
warrior near the end
of the King Arthur
days. He was related
to King Mark
His name means "child born in sadness" (by the way, it's often translated as Tristran). His mother died while giving birth to him, and her last words were to name her child Tristram. That would seem depressing, I know, but there's a whole huge love-story behind Tristram's parents, so you can understand why she was not happy about dying just then. His father died too, of course.
Anyway, all that aside, Tristram is best known for killing a dragon and doing many deeds of heroism which included winning the Gaelic princess Isolt (often translated Isolde or Isold) for his uncle, King Mark. Unfortunately, on the boat-ride home, he and Isolt accidentally drank a love-potion and fell madly in love with each other.
A whole lot of other adventures arose from this, but I'm not typing out the entire tale of Tristram and Isolt here. Wagner did an opera based on the drinking-love-potion part of the story, and the story itself is a pretty common myth you can find just about anywhere. Of course, I have to recommend that you read it....