grand duke of Luxembourg (1905–12), eldest son of grand duke Adolf of Nassau. Falling severely ill soon after his accession, he eventually on March 19, 1908, had his consort Maria Anna of Braganza named regent, or governor (Statthalterin). Also, having no sons and wishing to secure the succession of his daughters Marie-Adélaide and Charlotte, he had the Luxembourg Parliament allow succession in the female line.

The third son of King George III, he entered the Royal Navy at the age of 13, fought in the American Revolution, and, while serving in the West Indies, formed a close friendship with the future naval hero Horatio (afterward Viscount) Nelson. When he left the sea in 1790, however, he had become unpopular with many other fellow officers and had angered his father by his numerous love affairs. Between 1794 and 1807 he had 10 illegitimate children (surnamed FitzClarence) by the Irish comedienne Dorothea Jordan. His marriage (July 11, 1818) to Princess Adelaide of Saxe-Meiningen produced two daughters, both of whom died in infancy. On William's death, therefore, the British crown passed to his niece Princess Victoria, and the Hanoverian crown passed to his brother Ernest Augustus, duke of Cumberland.

The Duke became heir presumptive on the death (Nov. 6, 1817) of Princess Charlotte Augusta, only legitimate child of his older brother, the Prince Regent (afterward King George IV, reigned 1820–30). In April 1827 the new prime minister, George Canning, revived for him the office of lord high admiral, but he was forced to resign in August 1828, when the Duke of Wellington was premier. After succeeding George IV as king, William proved to be less brilliant but also less selfish and more attentive to official business than his brother had been.

In May 1832 the prime minister, Charles Grey, the 2nd Earl Grey, asked the King to create at least 50 new peers to overcome the House of Lords majority hostile to parliamentary reform. At first William refused, but after Wellington had failed to form a Tory (Conservative) ministry, Grey's Whigs resumed office with the King's written promise to create enough peers to carry the Reform Bill. The Lords, sufficiently threatened, allowed the bill to pass. As a consequence of redistricting, Sir Robert Peel's Tories were unable to gain a Commons majority in the election of January 1835; and from April of that year the King had to deal with an uncongenial Whig premier, William Lamb, 2nd Viscount Melbourne, whom he had previously dismissed.

On the death of Philip (1567) the partition of the Hessian lands among his four sons left William with little basis for a forceful foreign policy. Domestically, he sought a compromise between Lutherans and Calvinists. He was an outstanding organizer and a skilled economist. The Ökonomische Staat (1585), a territorial survey compiled for him, is a model of administrative statistics.

William also pursued scientific studies and perhaps owes his lasting fame to his research in astronomy. On friendly terms with the great Danish astronomer Tycho Brahe, he constructed numerous astronomical instruments and calculated many stellar positions.

prince of Orange and Nassau, general hereditary stadtholder of the United Netherlands.

The posthumous son of John William Friso of the house of Nassau-Dietz, William became stadtholder of Friesland and then later also of Groningen and of Gelderland, assuming his full functions in 1729–31. On March 25, 1734, he married Anne of Hanover (1709–59), eldest daughter of George II of Great Britain. By the extinction of other branches of the Ottonians of Nassau, he acquired a number of territories in Germany.

In April 1747, during the War of the Austrian Succession, the French invaded Dutch territory. A spontaneous popular movement arose, first in Zeeland, then in Holland, in Utrecht, and in Overijssel, for the elevation of William to the stadtholdership in these provinces, vacant since William III's death (1702), and to the ranks of captain general and admiral general. William was indeed appointed, and all his offices were made hereditary. The first man to be stadtholder of all seven provinces, William IV now had more power than any of his predecessors; but he proved incompetent as a leader, and peace was signed in 1748.

The Dutch people expected reforms to make the rule of the urban oligarchies in Holland less absolute. William, who was intelligent and industrious, made attempts to abolish the greatest abuses; but when he died, the most urgent problems were unsolved. He left a three-year-old son, William V.