According to tales first recorded in Old French in the 12th century, Yseut or Ysolt was an Irish princess betrothed to King Mark of Cornwall. After accidentally drinking a love potion, she became the lover of his nephew Tristan. Their tragic story, which was set in the Arthurian world, was popular during the Middle Ages and the name became relatively common in England at that time. It was rare by the 19th century, though some interest was generated by Richard Wagner's opera Tristan und Isolde (1865).
As a rarer (but older) masculine name it is probably derived from a surname: see Fay 1 or Fay 2.
The spelling was later altered to Cordelia when Geoffrey's story was adapted by others, including Edmund Spenser in his poem The Faerie Queene (1590) and Shakespeare in his tragedy King Lear (1606).
In England the name became rare after the Middle Ages, but it was revived in the 19th century, more commonly in the spelling Beatrice. Famous bearers include the British author and illustrator Beatrix Potter (1866-1943), the creator of Peter Rabbit, and Beatrix of the Netherlands (1938-), the former queen.
This name experienced a rise in popularity at the end of the 20th century. It was the most popular name for girls in England and Wales from 2011 to 2015.
As an English name it was highly popular from the Middle Ages until the 17th century. It was revived in the 19th century and was common into the 20th, but it fell into decline after the 1930s. It last appeared on the American top 1000 rankings in 1972.