George IV (George Augustus Frederick; 12 August 1762 – 26 June 1830) was King of the United Kingdom of Great Britain and Ireland and King of Hanover from 29 January 1820 until his death in 1830. At the time of his accession to the throne, he was acting as prince regent for his father, King George III, having done so since 5 February 1811 during his father's final mental illness.

George IV was the eldest child of King George III and Queen Charlotte. He led an extravagant lifestyle that contributed to the fashions of the Regency era. He was a patron of new forms of leisure, style and taste. He commissioned John Nash to build the Royal Pavilion in Brighton and remodel Buckingham Palace, and commissioned Jeffry Wyatville to rebuild Windsor Castle. George's charm and culture earned him the title "the first gentleman of England", but his dissolute way of life and poor relationships with his parents and his wife, Caroline of Brunswick, earned him the contempt of the people and dimmed the prestige of the monarchy. He excluded Caroline from his coronation and asked the government to introduce the unpopular Pains and Penalties Bill in an unsuccessful attempt to divorce her.

George's rule was tarnished by scandal and financial extravagance. His ministers found his behaviour selfish, unreliable and irresponsible, and he was strongly influenced by favourites. During most of George's regency and reign, Lord Liverpool controlled the government as prime minister of the United Kingdom. Liverpool's government presided over Britain's ultimate victory over Napoleon and negotiated a peace settlement with the French. After Liverpool's retirement, George was forced to accept Catholic emancipation despite opposing it. His only legitimate child, Princess Charlotte, predeceased him in 1817, as did his childless younger brother Prince Frederick in 1827, so he was succeeded by another younger brother, William IV.

George was born at St James's Palace, London, on 12 August 1762, the first child of King George III and Queen Charlotte. As the eldest son of a British sovereign, he automatically became Duke of Cornwall and Duke of Rothesay at birth; he was created Prince of Wales and Earl of Chester a few days later. On 18 September of the same year, he was baptised by Thomas Secker, Archbishop of Canterbury. His godparents were his maternal uncle Adolphus Frederick IV, Duke of Mecklenburg-Strelitz (for whom the Lord Chamberlain, William Cavendish, 4th Duke of Devonshire, stood proxy); his paternal grand-uncle Prince William, Duke of Cumberland; and his grandmother Augusta, Dowager Princess of Wales. George was a talented student and quickly learned to speak French, German and Italian, in addition to his native English.

At the age of 18, Prince George was given a separate establishment, and in dramatic contrast to his prosaic, scandal-free father, threw himself with zest into a life of dissipation and wild extravagance involving heavy drinking and numerous mistresses and escapades. He was a witty conversationalist, drunk or sober, and showed good, but grossly expensive, taste in decorating his residences. George turned 21 in 1783, and obtained a grant of £60,000 (equivalent to £9,124,000 today) from Parliament and an annual income of £50,000 (equivalent to £7,603,000 today) from his father. It was far too little for his wants—his stables alone cost £31,000 a year. He then established his residence in Carlton House, where he lived a profligate life. Animosity developed between the Prince and his father, who desired more frugal behaviour on the part of the heir apparent. The King, a political conservative, was also alienated by the Prince's adherence to Charles James Fox and other radically inclined politicians.

Soon after he reached the age of 21, the prince became infatuated with Maria Fitzherbert. She was a commoner (though granddaughter of a baronet), six years his elder, twice widowed, and a Roman Catholic. Nevertheless, the Prince was determined to marry her. This was in spite of the Act of Settlement 1701, which barred the spouse of a Catholic from succeeding to the throne, and the Royal Marriages Act 1772, which prohibited his marriage without the King's consent.

The couple went through a marriage ceremony on 15 December 1785 at Fitzherbert's house in Park Street, Mayfair. Legally the union was void, as the King's consent was not granted (and never even requested). However, Fitzherbert believed that she was the Prince's canonical and true wife, holding the law of the Church to be superior to the law of the State. For political reasons, the union was to remain secret and Fitzherbert promised not to reveal it. But, in spring 1786, covert allusions to the marriage appeared in the press, and several satirical prints depicted the clandestine marriage.

Prince George was plunged into debt by his exorbitant lifestyle. His father refused to assist him, forcing him to quit Carlton House and live at Fitzherbert's residence. In 1787, the Prince's political allies proposed to relieve his debts with a parliamentary grant. George's relationship with Fitzherbert was suspected, and revelation of the illegal marriage would have scandalised the nation and doomed any parliamentary proposal to aid him. Acting on Prince George's authority, the Whig leader Charles James Fox declared that the story was a calumny. Fitzherbert was not pleased with the public denial of the marriage in such vehement terms and contemplated severing her ties to George. He appeased her by asking another Whig, Richard Brinsley Sheridan, to restate Fox's forceful declaration in more careful words. Parliament, meanwhile, granted the Prince £161,000 (equivalent to £25,841,000 today) to pay his debts and £60,000 (equivalent to £9,630,000 today) for improvements to Carlton House.