Author
- Ogawa Tsunemitsu1
- Okçuzade Mehmet Sahî1
- Oliver Maillard1
- Order of Saint Michael1
- Order of the Argonauts of Saint Nicholas1
- Order of the Garter1
- Order of the Immaculate Conception1
- Orderic Vitalis1
- Oronce Finé1
- Orosius1
- Ortolanus1
- Osbern of Gloucester1
- Osman Süruri1
- Osman bin Keskin1
- Oswald Corda1
- Ottavio Strada1
- Ottmar Luscinius1
- Otto Ege1
- Otto di guardia e balia (Florence, Tuscany)1
- Otto of Passau1