Tristan da Cunha ( /ˈtrɪstən də ˈkuːnə/) is part of the British overseas territory of Saint Helena, Ascension and Tristan da Cunha which also includes Saint Helena 2,430 kilometres (1,510 mi) to its north, and equatorial Ascension Island even farther removed.

Tristan da Cunha is a remote volcanic group of islands in the south Atlantic Ocean and the main island of that group. It is the most remote inhabited archipelago in the world, lying 2,816 kilometres (1,750 mi) from the nearest land, South Africa, and 3,360 kilometres (2,088 mi) from South America. The territory consists of the main island of Tristan da Cunha itself, which measures about 11.27 kilometres (7.0 mi) across and has an area of 98 square kilometres (37.8 sq mi), along with the uninhabited Nightingale Islands and the wildlife reserves of Inaccessible Island and Gough Island. It has a permanent population of 275 (2009 figures).

The islands were first sighted in 1506 by Portuguese explorer Tristão da Cunha, although rough seas prevented a landing. He named the main island after himself, Ilha de Tristão da Cunha, which was later anglicised to Tristan da Cunha Island.

Tristan /ˈtrɪstən/ (Latin/Brythonic: Drustanus; Welsh: Drystan, Trystan; also known as Tristran, Tristram /ˈtrɪstrəm/, 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. The pair undergo numerous trials that test their secret affair.

Tristan makes his first medieval appearance in the early twelfth century in Celtic folklore circulating in the north of France, and Brittany in particular, which had close ancestral and cultural links with Cornwall by way of the ancient British kingdom of Dumnonia, as made clear in the story itself. Although the oldest stories concerning Tristan are lost, some of the derivatives still exist. Most early versions fall into one of two branches, the "courtly" branch represented in the retellings of the Anglo-Norman poet Thomas of Britain and his German successor Gottfried von Strassburg, and the "common" branch, including the works of the French poet Béroul and the German poet Eilhart von Oberge.