The American frontier comprises the geography, history, folklore, and cultural expression of life in the forward wave of American westward expansion since the colonial era. Enormous popular attention in the media focuses on the second half of the 19th century, a period sometimes called the Old West, or the Wild West. As defined by Hine and Faragher, "frontier history tells the story of the creation and defense of communities, the use of the land, the development of markets, and the formation of states." They explain, "It is a tale of conquest, but also one of survival, persistence, and the merging of peoples and cultures that gave birth and continuing life to America." Through treaties with foreign nations and native peoples, political compromise, technological innovation, military conquest, establishment of law and order, and the great migrations of foreigners, the United States expanded from coast to coast (Atlantic Ocean to Pacific Ocean), fulfilling advocates' belief in Manifest Destiny. In securing and managing the West, the U.S. federal government greatly expanded its powers, as the nation evolved from an agrarian society to an industrialized nation. First promoting settlement and exploitation of the land, by the end of the 19th century the federal government assumed stewardship of the remaining open spaces. As the American frontier passed into history, the myths of the west took firm hold in the imagination of Americans and foreigners alike.

Crazy Horse (Lakota: Tȟašúŋke Witkó (in Standard Lakota Orthography), literally "His-Horse-Is-Crazy" or "His-Horse-Is-Spirited"; ca. 1840 – September 5, 1877) was a Native American war leader of the Oglala Lakota. He took up arms against the U.S. Federal government to fight against encroachments on the territories and way of life of the Lakota people, including leading a war party at the Battle of the Little Bighorn in June 1876.

After surrendering to U.S. troops under General Crook in 1877, Crazy Horse was fatally wounded by a military guard while allegedly resisting imprisonment at Camp Robinson in present-day Nebraska. He ranks among the most notable and iconic of Native American tribal members and has been honored by the U.S. Postal Service with a 13¢ Great Americans series postage stamp.

Sources differ on the precise year of Crazy Horse's birth, but they agree he was born between 1840 and 1845. According to a close friend, 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 at about 1845.Encouraging Bear, an Oglala medicine man and spiritual adviser to the Oglala war leader, 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 his son "would soon have been thirty-seven, having been born on the South Cheyenne river in the fall of 1840".

Jesse Woodson James (September 5, 1847 – April 3, 1882) was an American outlaw, gang leader, bank robber, train robber and murderer from the state of Missouri and the most famous member of the James-Younger Gang. Already a celebrity when he was alive, he became a legendary figure of the Wild West after his death. Some recent scholars place him in the context of regional insurgencies of ex-Confederates following the American Civil War rather than a manifestation of frontier lawlessness or alleged economic justice.

Jesse and his brother Frank James were Confederate guerrillas during the Civil War. They were accused of participating in atrocities committed against Union soldiers. After the war, as members of one gang or another, they robbed banks, stagecoaches and trains. Despite popular portrayals of James as a kind of Robin Hood, robbing from the rich and giving to the poor, there is no evidence that he and his gang used their robbery gains for anyone but themselves.

The James brothers were most active with their gang from about 1866 until 1876, when their attempted robbery of a bank in Northfield, Minnesota, resulted in the capture or deaths of several members. They continued in crime for several years, recruiting new members, but were under increasing pressure from law enforcement. On April 3, 1882, Jesse James was killed by Robert Ford, who was a member of the gang living in the James house and who was hoping to collect a state reward on James' head.