} |} Leopold I (Leopold George Christian Frederick of Saxe-Coburg-Saalfeld, later of Saxe-Coburg and Gotha) (b. Coburg, 16 December, 1790 - d. Laeken/Laken, 10 December, 1865) was from 21 July, 1831 the first King of the Belgians. He was the founder of the Belgian line of the House of Saxe-Coburg-Gotha. His children included Leopold II of Belgium and Empress Carlota of Mexico.

He was the youngest son of Franz Frederick Anton, Duke of Saxe-Coburg-Saalfeld and Countess Augusta Reuss-Ebersdorf, and later became a prince of Saxe-Coburg and Gotha after the territorial swap by his father of Ehrenburg Castle in the Bavarian town of Coburg. He was also an uncle of Queen Victoria of the United Kingdom.

In 1795, as a mere child, Leopold was appointed colonel of the Izmaylovsky Imperial Regiment in Russia. Seven years later he became a major general. When Napoleonic troops occupied the Duchy of Saxe-Coburg in 1806 Leopold went to Paris. Napoléon offered him the position of adjutant, but he refused. Instead he took up a military career in the Imperial Russian cavalry. He campaigned against Napoléon, and distinguished himself at the Battle of Kulm at the head of his cuirassier division. In 1815 Leopold reached the rank of lieutenant general in the Imperial Russian Army.

In Carlton House on 2 May, 1816, he married Princess Charlotte Augusta of Wales, the only legitimate child of the British Prince Regent (later King George IV of the United Kingdom) and therefore heiress to the British throne, and was created a British field-marshal and Knight of the Garter. On 5 November, 1817, Princess Charlotte was delivered of a stillborn son; she herself died the following day. Had she lived, she would have become Queen of the United Kingdom on the death of her father, and Leopold presumably would have been her consort, and never chosen King of the Belgians. Despite Charlotte's death, the Prince Regent granted Prince Leopold the British style of Royal Highness by Order-in-Council on 6 April 1818. In honour of his first wife, Leopold and Louise-Marie, his second wife, named their first daughter Charlotte; she would become Empress Carlota of Mexico.

On 2 July, 1829, Leopold participated in nuptials of doubtful validity (a private marriage-contract with no religious or public ceremony) with the actress Caroline Bauer, created Countess of Montgomery, a cousin of his advisor, Christian Friedrich Freiherr von Stockmar. The 'marriage' reportedly ended in 1831 and the following year he married Louise-Marie.

After Belgium asserted its independence from the Netherlands on 4 October 1830, the Belgian National Congress, considered several candidates and eventually asked Leopold to become king of the newly formed country. He accepted and became "King of the Belgians" on 26 June, 1831. He swore allegiance to the constitution in front of the Sint Jacobs Church at Coudenbergh Place in Brussels on 21 July 1831. This day became the Belgian national holiday. Jules Van Praet would become his personal secretary. Less than two weeks later, on 2 August, the Netherlands invaded Belgium. Skirmishes continued for eight years, but in 1839 the two countries signed the Treaty of London establishing Belgium's independence. With the opening of the railway line between Brussels and Mechelen on 5 May, 1835, one of King Leopold's fondest hopes—to build the first railway in continental Europe—became a reality. In 1840 Leopold arranged the marriage of his niece Queen Victoria, the daughter of his sister Princess Victoria of Saxe-Coburg-Saalfeld, to his nephew Prince Albert of Saxe-Coburg and Gotha, son of his brother Ernst I, Duke of Saxe-Coburg and Gotha. Leopold would function as an advisor to his niece.

Leopold tried to pass laws to regulate female and child labour in 1842, but unsuccessfully. A wave of revolutions passed over Europe after the deposition of King Louis-Philippe from the French throne in 1848. Belgium remained neutral, mainly because of Leopold's diplomatic efforts.

In 1850, Leopold again lost a young wife, as Queen Louise-Marie died of tuberculosis at age 38. At 11:45am on 10 December, 1865, the king died in Laken. He lies buried in the Royal vault at the Church of Our Lady, Laken Cemetery, Brussels, Belgium.