- O’Henry the writer
- Bernardo O’Higgins, Chilean founding father with a province named after him
- Mrs. O’Leary whose cow started the Great Chicago Fire
- “Baba O’Riley”, one of the biggest hits of The Who
- Sinead O’Connor
- Ronnie O'Sullivan, top snooker player
- O’Henry the writer
- Bernardo O’Higgins, Chilean founding father with a province named after him
- Mrs. O’Leary whose cow started the Great Chicago Fire
- “Baba O’Riley”, one of the biggest hits of The Who
- Sinead O’Connor
- Ronnie O'Sullivan, top snooker player