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- Iulius Obsequens - writer
- Octavia - Major and Minor, two sisters of Augustus
- Claudia Octavia - daughter of Claudius
- Gaius Octavius - praetor, father of Augustus
- Gnaeus Octavius - two consuls
- Marcus Octavius - tribune
- Septimius Odenathus - king in east
- Quintus Lucretius Ofella (Afella) - commander
- Quintus Ogulnius Gallus - tribune
- Olympiodorus of Thebes - writer, emissary
- Olympiodorus the Younger - philosopher, astrologer
- Aurelius Opilius - freedman writer
- Lucius Opimius - consul
- Gaius Oppius - two
- Publilius Optatianus Porfyrius - poet
- Lucius Orbilius Pupillus - teacher, grammarian
- Paulus Orosius - late writer
- Publius Ostorius Scapula - Governor of Britain
- Titus Otacilius Crassus - praetor
- Marcus Salvius Otho - emperor
- Publius Ovidius Naso (Ovid) - poet
- Ovinius - tribune
Read more about this topic: List Of Ancient Romans