william iv (william henry; 21 august 1765 – 20 june 1837) was king of the united kingdom of great britain and ireland and of hanover from 26 june 1830 until his death. william, the third son of george iii of the united kingdom and younger brother and successor to george iv was the last person to rule both the united kingdom and hanover. his niece, victoria, ruled only the united kingdom, not hanover.