- O. Henry
- Octavia E. Butler
- Odetta
- Og Mandino
- Ogden Nash
- Olin Miller
- Oliver Cromwell
- Oliver Goldsmith
- Oliver Herford
- Oliver Wendell Holmes Jr.
- Oliver Wendell Holmes Sr.
- Olivia Wyndham
- Omar Khayyam
- Oprah Winfrey
- Orhan Pamuk
- Orison Swett Marden
- Orlando Aloysius Battista
- Orlando Bloom
- Orson Scott Card
- Orson Welles
- Oscar G. Hernandez
- Oscar Homolka
- Oscar Levant
- Oscar Wilde
- Oswald Avery
- Oswald Spengler
- Otto Ludwig
- Otto Rank
- Otto von Bismarck
- Ovid
- Owen D. Young
- Ozzy Osbourne