William IV may refer to the following monarchs:

• King William IV of the United Kingdom (reigned 1830-1837)
• Stadtholder William IV of The Netherlands, Prince of Orange, (1711–1751)
• When Prince William-Alexander , son of Queen Beatrix of the Netherlands, takes the throne he may do so under this regnal name as the last Dutch king with his name was William III.

Other famous noblemen known as William IV were:

• William IV "The Rich", a German nobleman

Guillermo IV | Guillaume IV | Willem IV