Big Elk, also known as Ontopanga (1765/75–1846/1848), was a principal chief of the Omaha tribe for many years on the upper Missouri River.

Big Elk led his people during a time of increasing changes, with threats from Sioux warfare, disease, and European-American encroachment.

He created alliances to protect his people and prepare for a future that he thought depended on a closer relationship with the United States.

The Omaha suffered from smallpox epidemics in the early nineteenth century and were decimated because of poor immunity to the European introduced disease and also because of sporadic immunisation programmes to the indigenous peoples, even though they were most at risk.

Big Elk was among the Native American allies of the United States during the War of 1812, through his relations with the French Creole trader Lucien Fontenelle from New Orleans, who served as an interpreter.

As the Omaha had a patrilineal kinship system, Logan Fontenelle was not considered to belong to the tribe because his father was white, a man of French-American ancestry from New Orleans.

As with many other Native American tribes, the Omaha were used to absorbing captives, orphans and honored allies into their culture as adopted members.

Similarly, Big Elk arranged or permitted two of his daughters to marry prominent European-American fur traders, with whom he wanted to make alliances to strengthen his family's connections.

[5] About 1823–24, Big Elk's daughter Me-um-bane married the fur trader Lucien Fontenelle, from a wealthy French Creole family in New Orleans.

[6] LaFlesche was highly assimilated and cultured, and married Mary Gale, daughter of an American surgeon and his Iowa wife.

During this period of major transition after the tribe moved to a reservation, he encouraged the Omaha to become educated in English, to accept Christianity, and to adopt some European-American ways.

He worked as an ethnologist for the Smithsonian Institution in a close partnership with the anthropologist Alice Fletcher; he wrote books and research about the Omaha and the Osage, and helped preserve their traditions.