Count William I of Hainaut was a nobleman who ruled during the 13th century. He was born around 1224 and became the Count of Hainaut in 1253. His reign was marked by efforts to strengthen his territory and maintain peace among the local nobility. He was also known for his involvement in the politics of the region, including alliances with neighboring territories. William I was a member of the House of Avesnes, which played a significant role in the history of Hainaut. He was the son of Count Baldwin of Avesnes and Countess Margaret of Hainaut. His leadership contributed to the stability and development of the region during a time of political change in medieval Europe.