- Octerlony, John A. (John Arvid), 1838-19051
- Oehme, F. G. (Ferdinand Gustav), 1826-1
- Osler, William, Sir, 1849-1919, author1
- Ostrom, Homer Irvin, 1852-19241
- Otis, Fessenden N. (Fessenden Nott), 1825-1900, author2
- Otis, George A. (George Alexander), 1830-18811
- Ott, Isaac, 1847-1916, author1