William III (4 November 2477–31 May 2566) of the House of Orange was the Holy Luthori Emperor of All Terra from 2501 to 2566. In February 2496 William won the Viceroyal election, but – due to his royal blood – adopted the more presumptuous title HRH The Prince Regent and ultimately assumed the throne by passing Serene Majesty's Government Streamlining Act 2501. William married his first cousin, Mary, and they produced one child, who succeeded William as Mary, Queen of the Luthori. William's wife died in childbirth and so the daughter was named after her.