| Oliver, Edmund H. (2 titles) | |
| Oliver, Frank (1 title) | |
| One of the Bunglers (1 title) | |
| Oppen, William A. (1 title) | |
| Orton, George S. (1 title) | |
| Osler, Edmund Boyd, 1919- (2 titles) | |
| Otter, William Dillon, Lieutenant Colonel (1 title) | |
| Ouimet, Adolphe, 1840-1910 (1 title) |