Theophil Henry Hildebrandt (24 July 1888 – 9 October 1980) was an American mathematician who did research on functional analysis and integration theory. Hildebrandt was born in Dover, Ohio, graduated from high school at age 14 and at age 17 in 1905 received his bachelor's degree from the University of Illinois. As a graduate student at the University of Chicago he earned his master's degree in 1906 and his PhD in 1910, with thesis A Contribution to the Foundations of Fréchet's Calcul Fonctionnel written under the direction of E. H. Moore. He became an instructor at the University of Michigan in 1909 and then a full professor in 1923, serving as chair of the mathematics department from 1934 until his retirement in 1957. His doctoral students include Ralph S. Phillips, Charles Earl Rickart,