Hermann Hagedorn (1882, New York City – d. 1964) was an American author, poet and biographer.
He was born in New York City and educated at Harvard University, where he was awarded the George B. Sohier Prize for literature, the University of Berlin, and Columbia University. From 1909 to 1911, he was an instructor in English at Harvard.
Hagedorn was a friend and biographer of Theodore Roosevelt. He also served as Secretary and Director of the Theodore Roosevelt Association from 1919 to 1957.