| Daniel Oakey | 1842–1888 | 1 |
| Eugene William Oates | 1845–1911 | 1 |
| Peregrin Obdržálek | 1825–1891 | 1 |
| Charles K. (Charles Kellogg) Ober | born 1856 | 1 |
| Frederick A. (Frederick Albion) Ober | 1849–1913 | 2 |
| Carlos María Ocantos | 1860–1949 | 1 |
| Adam Oehlenschläger | 1779–1850 | 1 |
| Marie Conway Oemler | 1879–1932 | 3 |
| Jacques Offenbach | 1819–1880 | 1 |
| George Offor | 1787–1864 | 4 |
| C. K. (Charles Kay) Ogden | 1889–1957 | 1 |
| George W. (George Washington) Ogden | 1871–1966 | 1 |
| Ruth Ogden | 1853–1927 | 1 |
| Frederic Austin Ogg | 1878–1951 | 3 |
| John Ogilvie | 1732–1813 | 1 |
| Georges Ohnet | 1848–1918 | 11 |
| Kakuzo Okakura | 1862–1913 | 1 |
| Edith Oland | 1878–1968 | 2 |
| Warner Oland | 1880–1938 | 2 |
| Frances Jenkins Olcott | 1872–1963 | 1 |
| Henry Steel Olcott | 1832–1907 | 1 |
| William Tyler Olcott | 1873–1936 | 1 |
| Old Elizabeth | born 1766 | 1 |
| Reuben Bertram Oldfield | 1878–1954 | 1 |
| Mr. (John) Oldmixon | 1673–1742 | 1 |
| Osborn H. (Osborn Hamiline) Oldroyd | 1842–1930 | 1 |
| Laurence Oliphant | 1829–1888 | 3 |
| Mrs. (Margaret) Oliphant | 1828–1897 | 8 |
| Charles A. (Charles Alexander) Oliver | 1858–1932 | 1 |
| Stephen Oliver | born 1950 | 3 |
| Alfred Ollivant | 1874–1927 | 3 |
| Gunnar Ollén | born 1913 | 1 |
| A. T. (Albert Ten Eyck) Olmstead | 1880–1945 | 1 |
| Everett Ward Olmsted | born 1869 | 2 |
| Warren Olney | 1841–1921 | 1 |
| Ernst W. (Ernst Wilhelm) Olson | 1870–1958 | 1 |
| Oscar Ludvig Olson | born 1872 | 1 |
| Omar Khayyam | 1048–1122 | 3 |
| František Omelka | 1904–1960 | 1 |
| George W. T. (George William Thomson) Omond | 1846–1929 | 2 |
| L. Onerva | 1882–1972 | 2 |
| Hanna Ongelin | 1848–1893 | 1 |
| Oliver Onions | 1873–1961 | 1 |
| Onkel Adam | 1804–1889 | 2 |
| Federico de Onís | 1885–1966 | 1 |
| E. Phillips (Edward Phillips) Oppenheim | 1866–1946 | 37 |
| James Oppenheim | 1882–1932 | 1 |
| L. (Lassa) Oppenheim | 1858–1919 | 2 |
| Frederick Burr Opper | 1857–1937 | 2 |
| Oliver Optic | 1822–1897 | 42 |
| Anders Orbeck | born 1891 | 1 |
| Alcide Dessalines d' Orbigny | 1802–1857 | 1 |
| William Dana Orcutt | 1870–1953 | 1 |
| Orczy, Emmuska Orczy, Baroness | 1865–1947 | 10 |
| Edith B. (Edith Bertha) Ordway | 1877–1944 | 1 |
| Alfredo Oriani | 1852–1909 | 2 |
| Orléans, Charlotte-Elisabeth, duchesse d' | 1652–1722 | 6 |
| Renee Richmond Huntley Ormsbee | born 1887 | 1 |
| Thomas H. (Thomas Hamilton) Ormsbee | 1890–1969 | 1 |
| John Ormsby | 1829–1895 | 45 |
| Robert Ornsby | 1820–1889 | 1 |
| Orpen, William, Sir | 1878–1931 | 1 |
| Charles Ebert Orr | 1861–1933 | 2 |
| John William Orr | 1815–1887 | 2 |
| Orr, Sutherland, Mrs. | 1828–1903 | 2 |
| Samuel Peter Orth | 1873–1922 | 3 |
| Ramalho Ortigão | 1836–1915 | 12 |
| George W. Orton | 1873–1958 | 1 |
| James Orton | 1830–1877 | 1 |
| Eliza Orzeszkowa | 1842–1910 | 1 |
| Henry Fairfield Osborn | 1857–1935 | 1 |
| Sherard Osborn | 1822–1875 | 1 |
| Dorothy Osborne | 1627–1695 | 1 |
| Duffield Osborne | 1858–1917 | 2 |
| Oliver T. (Oliver Thomas) Osborne | 1862–1940 | 1 |
| Lloyd Osbourne | 1868–1947 | 6 |
| Charles Grosvenor Osgood | 1871–1964 | 1 |
| Samuel Osgood | 1812–1880 | 1 |
| Edward Osler | 1798–1863 | 1 |
| Osler, William, Sir | 1849–1919 | 1 |