Kirtley Fletcher Mather (1888–1978) was an American geologist at Harvard University, and at one time, head of the geology department. He prepared a deposition for the Scopes "Monkey Trial", and helped Clarence Darrow rehearse his questioning of William Jennings Bryan.
He was an activist and author, and wrote multiple books on geology and related sciences. In 1937, he co-founded the Institute for Propaganda Analysis with Edward A. Filene and Clyde R. Miller.
A biography titled Cracking Rocks and Defending Democracy was written by Kennard Baker Bork, and published in 1994. Bork is an Alumni Professor of Geology at Denison University, Mather's alma mater. He also served on the board of trustees for Science Service, now known as Society for Science & the Public, from 1948-1956.
Mather had at least one daughter Florence Mather who married a fellow Ohioan Dr. Sherman Wengerd who taught petroleum geology at the University of New Mexico for many years. When Mather retired from Harvard University he moved to Albuquerque, New Mexico where he resided until his death in 1978 at the age of 90.