Crazy Horse (Lakota: Tȟašúŋke Witkó [tˣaˈʃʊ̃kɛ witˈkɔ], lit. 'His-Horse-Is-Crazy'; c. 1840 – September 5, 1877) was a Lakota war leader of the Oglala band. He took up arms against the United States federal government to fight against encroachment by White American settlers on Native American territory and to preserve the traditional way of life of the Lakota people. His participation in several famous battles of the Black Hills War on the northern Great Plains, among them the Fetterman Fight in 1866, in which he acted as a decoy, and the Battle of the Little Bighorn in 1876, in which he led a war party to victory, earned him great respect from both his enemies and his own people.

In September 1877, four months after surrendering to U.S. troops under General George Crook, Crazy Horse was fatally wounded by a bayonet-wielding military guard while allegedly resisting imprisonment at Camp Robinson in northwestern Nebraska. He was honored by the U.S. Postal Service in 1982 with a 13¢ Great Americans series postage stamp.

Sources differ on the precise year of Crazy Horse's birth, but most agree he was born between 1840 and 1845. According to Šúŋka Bloká (He Dog), he and Crazy Horse "were both born in the same year at the same season of the year," which census records and other interviews place in 1842. Ptehé Wóptuȟ’a (Encouraging Bear), an Oglala medicine man and spiritual adviser to Crazy Horse, reported that Crazy Horse was born "in the year in which the band to which he belonged, the Oglala, stole One Hundred Horses, and in the fall of the year," a reference to the annual Lakota calendar or winter count. Among the Oglala winter counts, the stealing of 100 horses is noted by Cloud Shield, and possibly by American Horse and Red Horse owner, as equivalent to the year 1840–41. Oral history accounts from relatives on the Cheyenne River Reservation place his birth in the spring of 1840. On the evening of his son's death, the elder Crazy Horse told Lieutenant H.R. Lemly that the year of birth was 1840.

Crazy Horse was born to parents from two different bands of the Lakota division of the Sioux, his father being an Oglala and his mother a Miniconjou. His father, born in 1810, was also named Tȟašúŋke Witkó (Crazy Horse). Crazy Horse was named Čháŋ Óhaŋ (Among the Trees) at birth, meaning he was one with nature.

One account said that after the son had reached maturity and shown his strength, his father gave him his name and took a new one, Waglúla (Worm). Another version of how the younger Crazy Horse acquired his name is that he took it after going through the haŋbléčheya ceremony. Crazy Horse's cousin (son of Hewáŋžiča, Lone Horn) was Maȟpíya Ičáȟtagya (Touch the Clouds). He saved Crazy Horse's life at least once and was with him when he died.

Rattling Blanket Woman or Tȟašína Ȟlaȟlá Wiŋ (1814–1844) was the daughter of Black Buffalo and White Cow (also known as Iron Cane). Her older siblings were Lone Horn (born 1790, died 1877) and Good Looking Woman (born 1810). Her younger sister was named Looks At It (born 1815), later given the name They Are Afraid of Her. The historian George Hyde wrote that Rattling Blanket Woman was Miniconjou and the sister of Spotted Tail, who became a Brulé head chief. She may have been a member of either of the family of Lone Horn, one of the leaders of the Miniconjou. She was said to be beautiful and a fast runner.

In 1844, while out hunting buffalo, Waglula helped defend a Lakota village under attack by the Crow. In gratitude he gave Waglula his two eldest daughters as wives: Iron Between Horns (age 18) and Kills Enemy (age 17). Corn's youngest daughter, Red Leggins, who was 15 at the time, requested to go with her sisters; all became Waglula's wives. When Waglula returned with the new wives, Rattling Blanket Woman, who had been unsuccessful in conceiving another child, thought she had lost favor with her husband and hanged herself. Waglula went into mourning for four years. Rattling Blanket Woman's sister, Good Looking Woman, came to offer herself as a replacement wife and stayed on to raise Crazy Horse. Other versions of the legend posit that she was grief-stricken by the deaths of those she knew; that her husband accused her of running off with her brother-in-law; or that she had an affair with a European-American man.

According to Frederick Hoxie's Encyclopedia of North American Indians, Crazy Horse was the third in his male line to bear the name of Crazy Horse. The love of his life was Tȟatȟáŋkasápawiŋ (Black Buffalo Woman), whom he courted, but she married another man named Mní Níča (No Water). At one point, Crazy Horse persuaded Black Buffalo Woman to run away with him. No Water borrowed a pistol and ran after his wife. When he found her with Crazy Horse, he fired at him, injuring him in the face and leaving a noticeable scar. Crazy Horse was married two times, first to Tȟašinásápawiŋ (Black Shawl) and second to Nellie Larrabee (Laravie). Nellie Larrabee was given the task of spying on Crazy Horse for the military, so the marriage is suspect. Only Black Shawl bore him any children, a daughter named Kȟokípȟapiwiŋ (They Are Afraid of Her), who died at age three.