William IV, Prince of Orange-Nassau (Willem Karel Hendrik Friso) was the first hereditary Stadtholder of all the United Provinces of the Netherlands.
He was born in Leeuwarden, Netherlands, the son of John William Friso, Prince of Orange, head of the Frisian branch of the House of Orange-Nassau, and of his wife Landgravine Marie Louise of Hesse-Kassel (or Hesse-Cassel). He was born six weeks after the death of his father.
William succeeded his father as Stadtholder of Friesland and also, under the regency of his mother until 1731, as Stadtholder of Groningen. In 1722 he was elected Stadtholder of Guelders. The four other provinces of the Dutch Republic:, Holland, Zeeland, Utrecht and Overijssel had in 1702 decided not to appoint a stadtholder after the death of stadtholder William III, issuing the history of the Republic into a period that is known as the Second Stadtholderless Period. In 1747 those four provinces also accepted William as their stadtholder.
In April 1747 the French army entered Flanders, threatening the Netherlands, which was weakened by internal division. The Dutch decided that their country needed a single strong executive, and turned to the House of Orange. William and his family moved from Leeuwarden to The Hague. On 4 May 1747, the States General of the Netherlands named William General Stadtholder of all seven of the United Provinces of the Netherlands, and made the position hereditary for the first time. He served as General Stadtholder of all the Netherlands until his death in 1751 at The Hague.