Dothraki is a conlang created by David Peterson for HBO's TV series Game of Thrones (an adaptation of George R. R. Martin‘s A Song of Ice and Fire). The language (as it is today) is an expansion of the sketch found in the first three books of A Song of Ice and Fire. It’s now a fully-developed language with a vocabulary of over 3,000 words (and growing).
The language is spoken by the Dothraki people, one of the concultures Martin created for his books. They are a race of nomadic horse warriors that live across the Narrow Sea on a large steppe-like grass plain known as the Dothraki Sea. Though they have a city (Vaes Dothrak), they go there only to trade, and never stay for long, ranging wide across the Dothraki Sea and stopping in at the cities that dot the coasts (the Free Cities, Slaver’s Bay, etc.).