Sitting Bull (Lakota: Tȟatȟáŋka Íyotake [tˣaˈtˣə̃ka ˈijɔtakɛ]; c. 1831–1837 – December 15, 1890) was a Hunkpapa Lakota leader who led his people during years of resistance against United States government policies. Sitting Bull was killed by Indian agency police accompanied by U.S. officers and supported by U.S. troops on the Standing Rock Indian Reservation during an attempt to arrest him at a time when authorities feared that he would join the Ghost Dance movement.

Before the Battle of the Little Bighorn, Sitting Bull had a vision in which he saw many soldiers, "as thick as grasshoppers", falling upside down into the Lakota camp, which his people took as a foreshadowing of a major victory in which many soldiers would be killed. About three weeks later, the confederated Lakota tribes with the Northern Cheyenne defeated the 7th Cavalry under Lt. Col. George Armstrong Custer on June 25, 1876, annihilating Custer's battalion and seeming to fulfill Sitting Bull's prophetic vision. Sitting Bull's leadership inspired his people to a major victory. In response, the U.S. government sent thousands more soldiers to the area, forcing many of the Lakota to surrender over the next year. Sitting Bull refused to surrender, and in May 1877, he led his band north to Wood Mountain, North-West Territories, now Saskatchewan. He remained there until 1881, when he and most of his band returned to U.S. territory and surrendered to U.S. forces.

After working as a performer with Buffalo Bill's Wild West show, Sitting Bull returned to the Standing Rock Agency in South Dakota. Because of fears that Sitting Bull would use his influence to support the Ghost Dance movement, Indian Service agent James McLaughlin at Fort Yates ordered his arrest. During an ensuing struggle between Sitting Bull's followers and the agency police, Sitting Bull was shot in the chest and head by Standing Rock policemen Lieutenant Bull Head (Tatankapah, Lakota: Tȟatȟáŋka Pȟá) and Red Tomahawk (Marcelus Chankpidutah, Lakota: Čhaŋȟpí Dúta), after the police were fired upon by Sitting Bull's supporters. His body was taken to nearby Fort Yates for burial. In 1953, his Lakota family exhumed what were believed to be his remains, reburying them near Mobridge, South Dakota, near his birthplace.

Sitting Bull was born on land later included in the Dakota Territory sometime between 1831 and 1837. In 2007, Sitting Bull's great-grandson asserted from family oral tradition that Sitting Bull was born along the Yellowstone River, south of present-day Miles City, Montana. He was named Ȟoká Psíče (Jumping Badger) at birth, and nicknamed Húŋkešni [ˈhʊ̃kɛʃni] or "Slow", an allusion to his careful and unhurried nature.

When Sitting Bull was 14 years old, he accompanied a group of Lakota warriors, which included his father and his uncle Four Horns, in a raiding party to take horses from a camp of Crow warriors. He displayed bravery by riding forward and counting coup on one of the surprised Crow, which was witnessed by the other mounted Lakota. Upon returning to camp, his father gave a celebratory feast at which he conferred his own name upon his son. The name, Tȟatȟáŋka Íyotake, in the Lakota language, roughly translates to "Buffalo Bull Who Sits Down", but Americans commonly refer to him as "Sitting Bull". Thereafter, Sitting Bull's father was known as Jumping Bull. At this ceremony before the entire band, Sitting Bull's father presented his son with an eagle feather to wear in his hair, a warrior's horse, and a hardened buffalo hide shield to mark his son's passage into manhood as a Lakota warrior.

During the Dakota War of 1862, in which Sitting Bull's people were not involved, several bands of eastern Dakota people killed an estimated 300 to 800 settlers and soldiers in south-central Minnesota in response to poor treatment by the government and in an effort to drive the whites away. Despite being embroiled in the American Civil War, the United States Army retaliated in 1863 and 1864, even against bands that had not been involved in the hostilities. In 1864, two brigades of about 2,200 soldiers under Brigadier General Alfred Sully attacked a village. The defenders were led by Sitting Bull, Gall and Inkpaduta. The Lakota and Dakota were driven out, but skirmishing continued into August at the Battle of the Badlands.

In September, Sitting Bull and about one hundred Hunkpapa Lakota encountered a small party near what is now Marmarth, North Dakota. They had been left behind by a wagon train commanded by Captain James L. Fisk to repair an overturned wagon. When he led an attack, Sitting Bull was shot in the left hip by a soldier. The bullet exited through the small of his back, and the wound was not serious.

From 1866 to 1868, Red Cloud, a leader of the Oglala Lakota, fought against U.S. forces, attacking their forts in an effort to keep control of the Powder River Country in present-day Montana. In support of Red Cloud, Sitting Bull led numerous war parties against Fort Berthold, Fort Stevenson, and Fort Buford and their allies from 1865 to 1868. The uprising has come to be known as Red Cloud's War.