William IV, Count of Holland, was a nobleman who ruled from 1345 until his death in 1346. He was a member of the House of Avesnes and succeeded his father, William III, Count of Holland. His reign was marked by conflicts with neighboring territories and internal struggles for power. William IV's rule was relatively short, and he faced challenges from rival factions, including the House of Hainaut. His death led to a succession crisis, which ultimately resulted in the rise of Holland as a significant political entity in the region.