List of people by name: A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
Oa-Ok - Ol-Oo - Op-Oz
- Oakie, Jack, (1903-1978), actor
- Oakley, Annie, (1860-1926), US sharpshooter
- Oates, John, (born 1949), musician ("Hall and Oates")
- Oates, Joyce Carol, (born 1938), US author, novelist
- Oates, Titus, (died 1706), British Protestant agitator
- Oberhauser, Josef, commander of the Belzec Extermination camp
- Oberheuser, Herta, (1911-1978), doctor, dubious experimenter
- Oberman, Sheldon, Canadian writer
- Obermeier, Gerlinde, dramatist, author
- Oberoi, Mohan Singh, (died 2002), hotelier, founder of the Oberoi chain of hotels
- Oberon, Merle, (1911-1979), actor
- Oberth, Hermann, (1894-1989), German physicist
- Oblak, Brane, football player
- Obote, Milton, twice Ugandan dictator
- Obradovic, Dositej, Serb
- Obree, Graham, broke world hour record (on a home-made bike)
- Obrenovic, Alexander, (1889-1903), king of Serbia
- Obrenovic, Milo, (1815-1839, 1858-1860), Serbian monarch
- O'Brian, Murchadh of the Isle, (1115-1137), king
- O'Brian, Patrick, (1914-2000), UK author
- O'Brien, Edna, novelist, member of Aosdána
- O'Brien, Flann, At Swim-Two-Birds
- O'Brien, Conan, (born 1963), US comedian and talk show host.
- O'Brien, Robert C, Mrs. Frisby and the Rats of NIMH
- O'Brien, Tim, (born 1946), American author
- O'Callaghan, Pat, Olympic gold medal/hammer, 1928, 1932
- O'Carolan, Turlough, 17th century harpist and composer ("Last of the Bards")
- Ocasek, Ric, (born 1949), musician ("The Cars")
- O'Casey, Sean, (1880-1964), playwright
- Ocasio, Ossie world champion boxer
- Ocean, Billy, (born 1950), US musician
- Ochino, Bernardino, (1487-1564)
- Ochoa, Ellen, astronaut
- Ochs, Phil, (1940-1976), musician
- Ochsenbein, Ulrich, (1811-1890), Swiss president
- Ochsner, Alton, surgeon & medical researcher
- Ockeghem, Johannes, (c.1430-c.1495), Belgian composer
- Ockels, Wubbo, astronaut
- Ockley, Simon, (1678-1720)
- O'Connell, Arthur, (1908-1981), actor
- O'Connell, Daniel, (1776-1847), Catholic Emancipation leader
- O'Connell, Kevin, member of Aosdána
- O'Connor, Bryan, astronaut
- O'Connor, Carroll, (1925-2001), US actor
- O'Connor, Des, British comedian
- O'Connor, Donald, (born 1925), singer, dancer, actor
- O'Connor, Flannery, (1925-1964), US author
- O'Connor, Frank, short story writer
- O'Conor, Herbert R, US governor
- O'Connor, Richard
- O'Connor, Sandra Day, (born 1930), US Supreme Court justice
- O'Connor, Sinead, (born 1966), Mother Bernadette, Irish singer
- O'Connor, Ulick, Aosdána
- O'Crohan, Thomas
- Octavianus, Gaius Julius Caesar (emperor Augustus)
- Oda Chikazane
- Oda Nagamasu, (1548 - 1622)
- Oda Nobuhide, (1510-1551), Japanese warlord
- Oda Nobunaga, (1534-1582), daimyo
- Oda Nobuyuki
- O'Daniel, W. Lee, (1939-1941), Texas Governor
- O'Day, Anita, (born 1919), musician
- Oddie, Bill, (born 1941), comedian
- Oddie, Tasker, (1870-1950)
- Oddsson, Davíð, (born 1991), prime minister
- Ode, Erik, (1910-1983), film director and actor
- Odell, Benjamin B., Jr, Republican, 1901-1904
- O'Dell, Scott, (1898-1989), Island of the Blue Dolphin
- Odets, Clifford, (1906-1963), dramatist, author
- Odetta, (born 1930), singer
- Odo of Châteauroux, scholastic philosopher
- Odo, Count of Paris, (died 866), Frankish king
- O'Donnell, Daniel, C and W singer
- O'Donnell, Peter, (born 1920), British creator of Modesty Blaise
- O'Donnell, Rosie, (born 1962), American actress, comedian and talk show host
- O'Donoghue, Brendan, Chief Herald of Ireland, 1997-date
- O'Doul, Lefty, (1897-1969), baseball star, restauranteur
- O'Duffy, General Eoin, leader of the Blueshirts
- O'Dywer, Mick, successful gaelic inter-county football manager
- O'Dwyer, William
- Oe, Kenzaburo, (born 1935), (Nobel Prize, 1994)
- Oe no Hiromoto, (1148-1225), senior statesman of the Kamakura shogunate
- Oeben, Jean Francois, (c.1721-1763)
- Oehlenschlager, Adam, (1779-1850), Danish poet
- Oerter, Al, (born 1936), Olympic Games gold medalist in track and field
- Offa of Essex, (Also joint leader) with Offa of Mercia??)
- Offa of Mercia, (died 796), king of Mercia, Bretwalda
- Offenbach, Jacques, (1819-1880), noted for his operettas
- Offord, John, Archbishop of Canterbury
- O'Flaherty, Liam, author
- Ogaryov, Nikolai, (1813-1877), author
- Ogen, Mart, poet
- Ogi, Adolf, (born 1942), Swiss president
- Ogilby, John, (1600-1676)
- Ogimachi, emperor of Japan
- Ogle, Benjamin, US governor
- Oglethorpe, James Edward, (1696-1785)
- Ogorevc, Blaz, poet
- O'Gorman, Juan, (1905-1982), Mexican artist
- O' Grady, Sean, (born 1959), world champion boxer
- Ohain, Hans von, (1911-1998), co-founder of the jet engine
- O'Hair, Madalyn Murray, US atheist
- OHanlon, George, (died 1989), actor/director.
- O'Hara, Catherine, actress
- O'Hara, Frank, poet
- O'Hara, Geoffrey, (1882-1967), Canadian songwriter
- O'Hara, Mary, harpist/singer
- O'Hara, Maureen, (born 1920), actress
- O'Hare, Edward, (born 1914), US pilot
- O'Herlihy, Dan, (born 1919), actor
- Ohm, Georg, (1789-1854), physicist
- Ohnesorg, Benno, (died 1967), German student of Roman languages and literature
- Oikarinen, Jarkko, Finnish creator of IRC
- Oistrakh, David, (1908-1974), violinist
- Oistrakh, Igor Davidovich, (born 1931), violinist
- Ojin, emperor of Japan
- Ojukwu, Odumegdu, leader of Biafra
- Okalik, Paul, (1947-1964), Greek King
- Okalik, Paul, premier of Nunavut
- O'Keeffe, Georgia, (1887-1986), American painter
- Okegwo, Ugonna
- O'Kelly, Sean T, (1882-1966), president
- Okun, Edward, Polish painter