Frederick Crayton Ainsworth (September 11, 1852 – June 5, 1934) was a surgeon in the United States Army who eventually rose to the position of Adjutant General. A gifted administrator, Ainsworth revolutionized government record-keeping methods following his initial appointment in 1886 to the Record and Pensions Division of the War Department, making them vastly more efficient. Ainsworth's talents were quickly recognized, and he was given administrative responsibility over more and more government departments, thus accumulating considerable power and eventually becoming the dominant figure in the Department of War.