The first known written version of the Tristan and Isolde story was done in France around 1235 by two men calling themselves Luce de Gat and Helie de Boron. Scattered references have been found to a lost older source, brought to France by English exiles. In some versions of the story, Tristan is called Tristram, and Isolde is called Iseult or Yseult, among other spellings.
The dynamic between Marke, Isolde, and Tristan is similar to Arthur, Guinevere, and Lancelot. Some scholars believe that they originated as the same source story, and then split apart into two versions. In some King Arthur books, Marke's kingdom coexists with Arthur and Camelot, and Lancelot meets Tristan and they compare notes.
Originally Ridley Scott was going to direct the film in the late-'70s, right after his debut film The Duellists (1977). He put the film aside to direct Alien (1979).
The best known version of the Tristan and Isolde legend is Richard Wagner's opera, written in 1859 and first performed in 1865. In Love Conquers All: The Making of Tristan + Isolde (2006), Sophia Myles said that when she was first offered the role of Isolde, she thought the movie was an adaptation of the opera.
After speaking about the film's making at the Gallifrey One event in February 2022, Sophia Myles noted on Twitter that James Franco "was difficult to work with," and that she "was forced into a tight spot because Franco was refusing to communicate with our Director Kevin Reynolds."