Haiti was a country located in the Caribbean.
The Seventh Doctor, Ace and Bernice Summerfield accidentally went there in 1915 when trying to visit Ernest Hemingway in nearby Key West, Florida. Once there, they met Francois Lacombe, a native of the Alsace region of France. While there, they prevented Gilles Lemaitre from summoning Cthulhu. (PROSE: White Darkness, PROSE: All-Consuming Fire)
According to the Seventh Doctor, it was a Haitian who first deciphered the Rihanssu language, which allowed a peace treaty to be drawn up, and ended an interstellar war with Earth in the 27th century. (PROSE: The Pit)