| Edward J. (Edward Joseph) O'Brien | 1890–1941 | 8 |
| F. P. O'Brien | born 1885 | 1 |
| Fitz James O'Brien | 1828–1862 | 1 |
| Frederick O'Brien | 1869–1932 | 2 |
| George O'Brien | 1892–1973 | 1 |
| R. Barry (Richard Barry) O'Brien | 1847–1918 | — |
| Seumas O'Brien | born 1880 | 1 |
| Michael O'Clery | 1575–1643 | 1 |
| J. C. (John Charles) O'Connor | 1853–1928 | 1 |
| T. P. (Thomas Power) O'Connor | 1848–1929 | 1 |
| J. F. X. (John Francis Xavier) O'Conor | 1852–1920 | 1 |
| Elliott O'Donnell | 1872–1965 | 3 |
| Standish O'Grady | 1846–1928 | 2 |
| Anne O'Hagan | 1869–1934 | — |
| Harvey Jerrold O'Higgins | 1876–1929 | 1 |
| John O'Mahony | 1816–1877 | 1 |
| James O'Meara | 1825–1903 | 1 |
| Elizabeth (Elizabeth Speakman) O'Neill | born 1877 | 1 |
| Eugene O'Neill | 1888–1953 | 4 |
| Rose Cecil O'Neill | 1874–1944 | 2 |
| John Boyle O'Reilly | 1844–1890 | 1 |
| M. V. (Michael Vincent) O'Shea | 1866–1932 | 1 |
| Vincent O'Sullivan | 1868–1940 | 1 |
| 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 |
| Ferdynand Antoni Ossendowski | 1878–1945 | 1 |
| Isabel Ostrander | 1883–1924 | 1 |
| Aleksandr Nikolaevich Ostrovsky | 1823–1886 | 2 |
| Hans Ostwald | 1873–1940 | 1 |
| Charles P. (Charles Pomeroy) Otis | 1840–1888 | 3 |
| James Otis | 1848–1912 | 8 |
| E. C. (Elise C.) Otté | 1818–1903 | 1 |
| Thomas Otway | 1652–1685 | 1 |
| Ouida | 1839–1908 | 11 |
| Xiu Ouyang | 1007–1072 | 2 |
| William Heysham Overend | 1851–1898 | 8 |
| Jacqueline Overton | 1887–1954 | 1 |
| John Henry Overton | 1835–1903 | 1 |
| William Hassell Overton | born 1868 | 1 |
| F. M. (Frances Mary) Owen | 1842–1883 | 1 |
| Luella Agnes Owen | 1852–1932 | 1 |
| Robert Emmett Owen | 1878–1957 | 10 |
| Wilfred Owen | 1893–1918 | 1 |
| Will Owen | 1869–1957 | 80 |
| John Oxenford | 1812–1877 | 1 |
| John Oxenham | 1852–1941 | 4 |
| J. Macdonald (James Macdonald) Oxley | 1855–1907 | 2 |
| John Oxley | 1783–1828 | 1 |
| Henry Oyen | 1883–1921 | 1 |