- O'Neal, J. W. C. (John William C.), 1821- author1
- Orr, Gustavus J., 1819-1887, author1
- Orrego Luco, Augusto, 1848-19331
- Ortega y Fonseca, Francisco.1
- OrvanĚanos, Domingo.1
- Otis, Fessenden N. (Fessenden Nott), 1825-19001
- Otis, Fessenden N. (Fessenden Nott), 1825-1900, author2