George IV was the son of King George III
, who became Prince Regent
during his father's insanity starting in 1811
when the younger George was 49, and succeeded to the actual kingship in 1820
George was a fairly wild young man; he spent much time with the Whig opponents of his father's political party and secretly married a Catholic woman, Maria Fitzherbert, which was illegal (and hence automatically void) under the Royal Marriages Act 1772. He also got into a huge amount of debt (more than 250,000 pounds), which originally neither his father or Parliament would help him out of. George sold his racehorses and reduced the number of his servants, announcing that he would live in seclusion until he had paid off his debt. This made a good impression on his father and Parliament and both decided to allot him some additional money, but as soon as George got his hands on it, he was off to his extravagant pastimes again.
During George III's earlier bouts of madness, his sons were encouraged to marry legally and produce heirs; the promise of getting an increase of income from a marriage settlement led George to agree to marry his first cousin Caroline of Brunswick. George and Caroline couldn't stand each other at their first meeting, but the marriage went ahead in 1795. (George only got through the ceremony by getting drunk, and Caroline reported that he spent his wedding night passed out on the floor.) The two did manage to produce a daughter, Charlotte, but separated soon after.
While George was Prince Regent, Napoleon was defeated at Waterloo and England's power in European affairs increased. Unfortunately, George's daughter Charlotte died in childbirth in 1817 at the age of 21, and as George seemed unlikely to have any more legitimate children, his brothers rushed to get married and provide heirs.
When George IV finally officially took the throne in 1820, he wanted to keep Caroline (who had been living in Europe) from coming back to England and insisting on being treated as Queen. He actually forced his ministers to bring in legislation into Parliament to try and deprive her of the title of Queen and to dissolve the marriage completely. (Cartoons circulated of Caroline and her supposed Italian lover during the Queen Caroline crisis.) The bill was eventually dropped, but the humilation exacerbated Caroline's physical troubles and she died, probably of chronic bowel troubles, in 1821.
George, unusually for English monarchs of the era, visited all his territories, including Ireland, Scotland, Hanover. During his reign he tried to block the Catholic Emancipation Act, which would allow Catholics some freedoms and access to positions that formerly only Protestants could have, from being passed. He died on 26 June 1830 and was succeeded by his brother William IV.