As of February 2022, how many kings of England (and later the UK) have used the regal name William?

As of 2022 there have been four king Williams of England and the UK.

William I (c. 1028 – 9 September 1087), usually known as William the Conqueror, was King of England from 25 December 1066 – 9 September 1087. William died at Rouen after a fall from his horse whilst besieging the French city of Nantes. He is buried at Caen.

William II (c. 1056 – 2 August 1100) was King of England from 26 September 1087 until his death in 1100. He never married and was killed in the New Forest by a stray arrow whilst out hunting.

William III (4 November 1650 – 8 March 1702), also widely known as William of Orange, was King of England, Ireland, and Scotland from 1689 until his death in 1702. William died of pneumonia, a complication from a broken collarbone following a fall from his horse, Sorrel.

William IV (William Henry; 21 August 1765 – 20 June 1837) was King of the United Kingdom of Great Britain and Ireland and King of Hanover from 26 June 1830 until his death in 1837. William succeeded his elder brother George IV, becoming the last king and penultimate monarch of Britain's House of Hanover.