Robert Daniel Carmichael (1879–1967) was a leading American mathematician. Carmichael was born in Goodwater, Alabama. He attended Lineville College, receiving his B.A. in 1898, while working towards his Ph. D at Princeton University, which he earned in 1911. His thesis was written under G.D. Birkhoff and is considered the first significant American contribution to differential equations. He then taught at Indiana University from 1911 to 1915, and at the University of Illinois from 1915 until 1947. Carmichael is known for his work on what are now called Carmichael numbers, Carmichael's theorem, and the Carmichael function, all significant in number theory and the study of primes.