O
- Frederick Oakeley
- Michael Oakeshott
- Joyce Carol Oates
- Stephen B. Oates
- Boy Scout Oath
- Tunde Obadina
- Barack Obama
- Michelle Obama
- Barack Obama campaign slogan
- Barbara O'Brien
- Conan O'Brien
- Edna O'Brien
- Flann O'Brien
- John A. O'Brien
- Kate Cruise O'Brien
- Miles O'Brien
- "The O.C."
- Sean O'Casey
- Adolph S. Ochs
- Simon Ockley
- Daniel O'Connell
- Flannery O'Conner
- Flannery O'Connor
- Len O'Connor
- Sandra Day O'Connor
- Octavian
- Clifford Odets
- Odetta
- Major Michael Davis O'Donnell
- Michael O'Donoghue
- Roger von Oech
- Barbara Oehlberg
- Charleton Ogburn Jr.
- Howard Ogden
- William Ogden
- David Ogilvy
- Madalyn Murray O'Hair
- John O'Hara
- Theodore O'Hara
- Georgia O'Keeffe
- Oklahoma State Law
- Daniel Okrent
- Arthur M. Okun
- Old Farmer's Almanac
- William Oldys
- Nathan Oliveira
- Frederick Oliver
- Mary Oliver
- Laurence Olivier
- Ken Olsen
- Austin O'Malley
- Omar I
- Aristotle Onassis
- Jacqueline Kennedy Onassis
- Carlotta O'Neill
- Eugene O'Neill
- Molly O'Neill
- Yoko Ono
- David Opfer
- Amelia Opie
- James Oppenheim
- Frank Oppenheimer
- J. Robert Oppenheimer
- A. R. Orage
- Robert Orben
- Baroness Orczy
- Robert Oren
- Origen
- Jules Ormont
- Brian O'Rourke
- P.J. O'Rourke
- Leonard Orr
- Raoul Ortega
- Orthodox Church
- Joe Orton
- George Orwell
- Ronald E. Osborn
- Adam Osborne
- Alex F. Osborne
- John Osborne
- Ozzy Osbourne
- Charles Grosnevor Osgood
- Charles Osgood
- Arthur William Edgar O'Shaughnessy
- William Osler
- John L. O'Sullivan
- Lee Harvey Oswald
- Willie Stargell, Also attributed to Hank Sauer, Pete Rose, Ted Williams, others
- James Otis
- Thomas Otway
- Ouida
- Fulton Oursler
- P. D. Ouspensky
- George Outram
- Thomas Overbury
- Mark Overby
- Harry Allen Overstreet
- Francis O'Walsh
- David Owen
- Gareth Owen
- John Owen
- Robert Owen
- Wilfred Owen
- Terrell Owens
- David Ownen
- John Oxenham
- Oxford Union Society
- Amedee Ozenfant
- Cynthia Ozick
- Ozymandelson
