William A. Peffer (September 10, 1831 - October 6, 1912) was a United States Senator from Kansas. Born in Cumberland County, Pennsylvania, he attended the public schools and commenced teaching at the age of fifteen. He followed the gold rush to San Francisco, California in 1850 and moved to Indiana in 1853, Missouri in 1859, and Illinois in 1862. During the Civil War he enlisted in the Union Army as a private, was promoted to second lieutenant, and served as regimental quartermaster and adjutant, post adjutant, judge advocate of the military commission, and department quartermaster in the engineering department at Nashville. He was mustered out of the service in 1865. While in the Army he studied law, and was admitted to the bar in 1865, commencing practice in Clarksville, Tennessee. He moved to Fredonia, Kansas in 1870 and continued the practice of law, and purchased and edited the Fredonia Journal.
Peffer was a member of the Kansas Senate from 1874 to 1876 and moved to Coffeyville, Kansas, where he edited the Coffeyville Journal in 1875 and also practiced law. He was a presidential elector on the Republican ticket in 1880 and was editor of the Kansas Farmer at Topeka in 1881. He was elected as a Populist to the U.S. Senate and served from March 4, 1891, to March 3, 1897; he was an unsuccessful candidate for reelection in 1896. While in the Senate, he was chairman of the Committee to Examine Branches of the Civil Service (Fifty-third and Fifty-fourth Congresses). He was, in 1898, an unsuccessful candidate for Governor of Kansas, and afterward engaged in literary pursuits. Peffer died in Grenola, Kansas in 1912 and was interred in Topeka Cemetery.