William IV of Aquitaine was a nobleman who ruled the region of Aquitaine in southwestern France during the 10th century. He was a member of the powerful House of Poitiers and played a significant role in the politics of medieval France. His reign was marked by efforts to strengthen his territory and maintain its independence from the influence of the French crown. William IV was known for his military prowess and his ability to navigate the complex feudal system of the time. He was also involved in various alliances and conflicts with neighboring lords, which were common during this turbulent period in European history.