Charles Alexander Eastman (February 19, 1858 – January 8, 1939, born Hakadah and later named Ohíye S'a, sometimes written Ohiyesa) was an American physician, writer, and social reformer.

After working as a physician on reservations in South Dakota, he became increasingly active in politics and issues on Native American rights.

He was the last of five children of Wakantakawin, a mixed-race woman also known as Winona (meaning "First-Born Daughter" in the Dakota language), or Mary Nancy Eastman.

Winona was the only child of Wakháŋ Inážiŋ Wiŋ (Stands Sacred) and Seth Eastman, a U.S. Army career officer and illustrator, who married at Fort Snelling in 1830, where he was stationed.

Stands Sacred was the fifteen-year-old daughter of Cloud Man, a Santee Dakota chief of French and Mdewakanton descent.

His maternal grandmother Stands Sacred (Wakháŋ Inážiŋ Wiŋ) and her family took the boy with them as they fled from the warfare into North Dakota and Manitoba, Canada.

Eastman and his older brother John attended a mission then a preparatory school, Kimball Union Academy from 1882 to 1883, and college.

He attended medical school at Boston University, where he graduated in 1890 and was among the first Native Americans to be certified as a European-style doctor, a year after Carlos Montezuma (Yavapai/Apache) and Suzette LaFlesche (Omaha/Iowa) earned their degrees.

[10] According to Ruth Ann Alexander, Elaine is not given enough credit for his success, although she worked intensively on Charles's stories as a way both to share his life and to use her own literary talent as his typist and editor.

Some Native scholars suggest that in fact, there is both content and style in Eastman's writing that reflects Indigenous techniques.

Inspired by his writings, Ernest Thompson Seton sought Eastman's counsel in forming the Woodcraft Indians, which became a popular group for boys.

[17] Luther Gulick also consulted with Eastman to assist him and his wife Charlotte to develop the Camp Fire Girls.

With his fame as an author and lecturer, Eastman promoted the fledgling Boy Scouts and Camp Fire Girls.

In 1903, President Theodore Roosevelt assigned Eastman to helping Sioux (Dakota, Nakota, Lakota) tribal members to choose English legal names, in order to prevent individuals and families from losing allotted lands due to confusion over cultural naming conventions and spellings.

The Calvin Coolidge administration (1923-1929) invited Eastman to the Committee of 100, a reform panel examining federal institutions and activities dealing with Indian nations.

The committee recommended that the government conduct an in-depth investigation into reservation life (health, education, economics, justice, civil rights, etc.).

In 1925, the Office of Indian Affairs asked Eastman to investigate the death and burial location of Sacagawea, the young woman who guided and interpreted for the Lewis and Clark Expedition in 1805.

[citation needed] However, based on a recently discovered journal of 1812–1813, modern historians believe that Sacagewea died in 1812 as a result of an illness following the birth of her daughter Lisette at Fort Lisa (North Dakota).

Eastman's many jobs, failure to provide financially for the family, and absences on the lecture circuit, put increasing strain on the couple.

Although the paternity of this child, named Bonno by her mother, was never proven, letters from Henrietta and from Elaine strongly point to Charles Eastman as the father.

[21][19] Charles Eastman built a cabin on the eastern shore of Lake Huron, where he spent his later-year summers.

[23][24] Elaine Goodale Eastman spent the remainder of her life living with two of her daughters and their families in Northampton, Massachusetts.