William IV was the son of King George III
and the younger brother of George IV
, who he succeeded on the throne
at the age of 65.
William was born in 1765, the third son, and actually went to sea as an ordinary seaman at the age of 14. On his father's orders, he received no special privileges, but gradually rose through the ranks, and struck up a friendship with Admiral Lord Horatio Nelson. In 1785 after having been given the rank of Duke of Clarence, he took a seat in the House of Lords and was appointed Rear Admiral of the Blue, putting an end to his active service, though he continued to hold high naval positions.
William had had a long-running relationship and 10 children with an actress, Mrs. Jordan, but after his niece Charlotte's death, the royal family needed an heir in the next generation, and William married Adelaide of Saxe-Meiningen. The two got along very well, but their children were either miscarried or died in infancy.
William became king on his brother's death in 1830. He was pretty eccentric despite Adelaide's attempts to keep him from looking silly, but could sometimes be very shrewd. He helped pass the Reform Bill, which allowed more people to vote, by sending around a letter to the Tory noblemen who would have voted against it (apparently threatening to create more nobles who would be Whigs), causing 100 Tory Lords to abstain from voting on the bill. The Whigs were then able to pass it.
William's niece Victoria was the only heir to the throne, but William hated her mother and often said he hoped he would live long enough to see Victoria turn 18 and be able to rule without her mother as regent. His wish was granted, and he died on 20 June 1837 and was succeeded by the 18-year-old Victoria.