Count William I of Holland, also known as William I of the House of Avesnes, ruled from 1256 until his death in 1257. He was a significant figure in the history of the County of Holland, which is now part of the Netherlands. His reign was marked by efforts to strengthen the authority of the count and manage conflicts with local nobility. William I was the son of Count Floris IV of Holland and Matilda of Brabant. His short rule ended when he died unexpectedly, leading to a succession crisis. His legacy includes the continued development of the Holland region during a time of political change in medieval Europe.