William IX, called the Troubadour, was the Duke of Aquitaine and Gascony and Count of Poitou between 1086 and his death. He was also one of the leaders of the Crusade of 1101. Though his political and military achievements have a certain historical importance, he is best known as the earliest troubadour—a vernacular lyric poet in the Occitan language—whose work survives.

The Duke of Aquitaine was the ruler of the medieval region of Aquitaine under the supremacy of Frankish, English, and later French kings.