William Penn Adair (1830–1880) was a Cherokee leader and Confederate colonel. He was a slave holder. Many Cherokee freedmen carried his surname as he and his father carried many slaves to Indian Territory.
William Penn Adair was born on April 15, 1830 in the old Cherokee Nation in New Echota, Georgia. His parents were George Washington Adair (1806-1862) and Martha (née Martin) Adair. He attended Cherokee schools in Indian Territory, studying law. He was a Freemason, belonging to the Vinita Lodge No. 5, which was chartered in 1875. He was described as being "six foot and two inches in height, magnetic, logical and frankly agreeable, the ablest and most brilliant of all Cherokees.
Adair's first wife was Sarah Ann McNair. His second was Susannah "Sue" McIntosh Drew. He lived on the Grand River in what is now Adair, Oklahoma.
During the Civil War he served in the Confederate States Army, first in the First Regiment of Cherokee Mounted Volunteers, under General Stand Watie. Adair rose in rank to colonel and organized the Second Cherokee Mounted Volunteers.
Adair served the Cherokee Nation in many capacities. He was a senator, a justice of the Cherokee Supreme Court, delegate to Washington, DC, and assistant principal chief. He served as the Senator from the Flint District from 1855-1860 and Senator from the Saline District from 1869-1874. In 1879, he was elected as Assistant Chief. Throughout the 1860s and 1870s, Adair served as a delegate to Washington.
He was a vocal advocate for the rights of the Texas Cherokees. In 1873, he and Clement Neely Vann co-authored the book, History of the Claim of the Texas Cherokees, in which they wrote on behalf of "the Texas Cherokees and Affiliated Bands."