Leopold II (French: Léopold Louis Philippe Marie Victor, Dutch: Leopold Lodewijk Filips Maria Victor) (9 April 1835 – 17 December 1909) was King of the Belgians. Born in Brussels the second (but eldest surviving) son of Leopold I and Louise-Marie of Orléans, he succeeded his father to the throne in 1865 and remained king until his death. He was the brother of Empress Carlota of Mexico and first cousin to Queen Victoria of the United Kingdom.

Leopold is chiefly remembered as the founder and sole owner of the Congo Free State, a private project undertaken by the King. He used Henry Morton Stanley to help him lay claim to the Congo, an area now known as the Democratic Republic of the Congo. The Powers at Berlin Conference agreed to set up the Free State in 1885, on condition that the inhabitants were to be brought into the modern world and that all nations be allowed to trade freely. From the beginning, however, Leopold essentially ignored these conditions and ran the Congo brutally, by proxy through a mercenary force, for his own personal gain. He extracted a personal fortune from the Congo, initially by the collection of ivory, and after a rise in the price of rubber in the 1890s by forcing the native population to collect sap from rubber plants. His harsh regime was directly or indirectly responsible for the death of millions of people. The Congo became one of the most infamous international scandals of the early 20th century, and Leopold was ultimately forced to relinquish control of it to the government of Belgium.

Leopold II married teenage Habsburg duchess Marie Henriette Anne of Austria in Brussels on 22 August 1853. Leopold was too ill to attend his own wedding, and sent his brother-in-law, Archduke Charles, to stand in for him. Unfortunately for the sexually naïve Marie Henrietta, who had gone to her wedding bed armed only with instructions to submit to her husband’s wishes, Leopold sufficiently recovered to attend the honeymoon. They had four children. Leopold II was also the father of two illegitimate sons. Their mother was Blanche Zélia Joséphine Delacroix, aka Caroline Lacroix, a prostitute with whom the King engaged in a religious ceremony on 12 December/14 December 1909, with no validity under Belgian law, at the Pavilion of Palms, Royal Palace of Laken, in Brussels, five days before his death. The Priest of Laeken Cooreman performed the ceremony. These sons were adopted in 1910 by Lacroix's second husband, Antoine Durrieux.

He was the 975th Knight of the Order of the Golden Fleece in Austria, the 748th Knight of the Order of the Garter in 1866 and the 69th and 321st Grand Cross of the Order of the Tower and Sword.

On 15 November 1902, Italian anarchist Gennaro Rubino attempted to assassinate Leopold, who was riding in a royal cortege from a ceremony in memory of his recently deceased wife, Marie Henriette. After Leopold's carriage passed, Rubino fired three shots at the King; the shots missed Leopold and Rubino was immediately arrested.

In Belgian domestic politics, Leopold emphasized military defense as the basis of neutrality, but he was unable to obtain a universal conscription law until on his death bed. He died in Laeken on 17 December 1909, and was interred in the royal vault at the Church of Our Lady, Laeken Cemetery, Brussels. He was succeeded as King of the Belgians by his nephew Albert, son of his brother Philippe.

Leopold fervently believed that overseas colonies were the key to a country's greatness, and he worked tirelessly to acquire colonial territory for Belgium. Neither the Belgian people nor the Belgian government were interested, however, and Leopold eventually began trying to acquire a colony in his private capacity as an ordinary citizen. The Belgian government lent him money for this venture. After a number of unsuccessful schemes for colonies in Africa or Asia, in 1876 he organized a private holding company disguised as an international scientific and philanthropic association, which he called the International African Society. In 1878, under the auspices of the holding company, he hired the famous explorer Henry Morton Stanley to establish a colony in the Congo region. Much diplomatic maneuvering resulted in the Berlin Conference of 1884–85, at which representatives of fourteen European countries and the United States recognized Leopold as sovereign of most of the area he and Stanley had laid claim to. On 5 February 1885, the result was the Congo Free State (later becoming, successively, the Belgian Congo, the Republic of the Congo, Zaire, and now the Democratic Republic of the Congo or DRC — not to be confused with Republic of the Congo formerly owned by France), an area 76 times larger than Belgium, which Leopold was free to rule as a personal domain through his private army, the Force Publique.

Abandoning the promises of the Berlin Conference in the late 1890s Forced labor was extorted from the natives. The abuses suffered were horrific not only in the rubber industry, including the effective enslavement and sometimes mutilation of the native population. Missionary John Harris of Baringa, for example, was so shocked by what he had come across that he wrote to Leopold's chief agent in the Congo saying: "I have just returned from a journey inland to the village of Insongo Mboyo. The abject misery and utter abandon is positively indescribable. I was so moved, Your Excellency, by the people's stories that I took the liberty of promising them that in future you will only kill them for crimes they commit." Estimates of the death toll range from a realistic two million to an unlikely fifteen million. Determining precisely how many people died is next to impossible as accurate records were not kept.

Adam Hochschild devotes a chapter of his book, King Leopold's Ghost, to the problem of estimating the death toll. He cites several recent lines of investigation, by anthropologist Jan Vansina and others, examining local sources, from police records, religious records, oral traditions, genealogies, personal diaries, and "many others", which generally agree with the assessment of the 1919 Belgian government commission: roughly half the population perished during the Free State period. Since the first official census by the Belgian authorities in 1924 put the population at about 10 million, that implies a rough estimate of 10 million dead. This assessment has been challenged by more recent studies of the 1919 commission's methods of estimation. Smallpox and sleeping sickness also devastated the population. By 1896 the sleeping sickness had killed up to 5,000 Africans in the village of Lukolela on the Congo River. The mortality figures were gained through the efforts of Roger Casement, who found only 600 survivors of the disease in Lukolela in 1903.

Reports of outrageous exploitation and widespread human rights abuses led to international outcry in the early 1900s. The campaign to examine Leopold's regime, led by British diplomat Roger Casement and former shipping clerk E.D. Morel under the auspices of the Congo Reform Association, became the first mass human rights movement. Supporters included American writer Mark Twain, who wrote a stinging political satire entitled King Leopold's Soliloquy, in which the King supposedly argues that bringing Christianity to the country outweighs a little starvation. Rubber gatherers were tortured, maimed and slaughtered until the turn of the century, when the Western world forced Brussels to call a halt. Arthur Conan Doyle also blasted the 'rubber regime' in his 1908 work 'The Crime of the Congo', written to aid the work of the Congo Reform Association. Doyle contrasted Leopold's rule to the British rule of Nigeria, arguing decency required that those who ruled primitive peoples to be concerned first with their uplift, not how much could be extracted from them. Doyles work is the most complete contemporary account of the Congo scandal. It should be noted that, as Hochschild describes in King Leopold's Ghost, Imperial Germany and to a lesser extent France and Portugal adopted the Congo methods to some extent in those parts of their colonies where natural rubber occurred.

Finally, in 1908, the Belgian parliament compelled the King to cede the Congo Free State to Belgium. Emperor Franz Joseph of Austria-Hungary once described his fellow ruler as a "thoroughly bad man".

Leopold II is still a controversial figure in the Democratic Republic of Congo; in 2005 his statue was taken down just hours after it was re-erected in the capital, Kinshasa. The Congolese culture minister, Christoph Muzungu, decided to reinstate the statue, pointing out the sense of liberating progress that had marked the beginning of the Free State and arguing people should see the positive aspects of the king as well as the negative. But just hours after the six metre (20 ft) statue was erected in the middle of a roundabout near Kinshasa's central station, it was taken down again, without explanation. The Congo continues, however, to use a variation of the Free State flag, which it adopted after dropping the name and flag of Zaire.

Though extremely disliked by his subjects at the end of his reign — his funeral cortege was booed — Leopold II is remembered today by many Belgians as the "Builder King" (Koning-Bouwer in Dutch, le Roi-Bâtisseur in French) because he commissioned a great number of buildings and urban projects, mainly in Brussels, Ostend and Antwerp. These buildings include the Royal Glasshouses in the grounds of the Palace at Laken, the Japanese Tower, the Chinese Pavilion, the Musée du Congo (now called the Royal Museum for Central Africa), and their surrounding park in Tervuren, the Cinquantenaire in Brussels, and the Antwerp railway station hall. He also built an important country estate in Saint-Jean-Cap-Ferrat on the French Riviera, including the Villa des Cèdres, which is now a botanical garden. These were all built using the profits from the Congo. In 1900, he created the Royal Trust, by which means he donated most of his property to the Belgian nation.

After the King transferred his private colony to Belgium, there was, as Adam Hochschild puts it in King Leopold's Ghost, a "Great Forgetting". Hochschild records that, on his visit to the colonial Royal Museum for Central Africa in the 1990s, there was no mention of the atrocities committed in the Congo Free State, despite the museum's large collection of colonial objects. Another example of this "Great Forgetting" may be found on the boardwalk of Blankenberge, a popular coastal resort, where a monument shows a colonialist bringing "civilization" to the black child at his feet. However an activist group cut off the hands of a statue of Leopold II in Ostend to protest the Congo atrocities.