| comment/origin etc. | famous bearer of this name | |
| Oakley | ||
| Obadja | (scriptural) | |
| Obal | (scriptural) | |
| Obed | (scriptural) | |
| Oberon | ||
| Obi | (african) | |
| Obie | ||
| Ocie | ||
| Octavian | (see Octavianus) | |
| Octavianus | (Augustus: his first name was Octavius, after acception of Caesars heritage he took Octavianus, but it was changed later to Augustus to celebrate him) |
|
| Octavio | (see Octavianus) | |
| Octavious | (see Octavianus) | |
| Octavius | (see Octavianus) | |
| Odaniz | ||
| Oddbjörn | ||
| Odell | ||
| Odhrán | (irish) | |
| Odie | ||
| Odilo | ||
| Odilon | ||
| Odis | ||
| Odisseas | (greek, version) | |
| Odo | (Odo di Colonna, later Pope Martin V) | |
| Odoacer | ||
| Odolricus | (medieval) | |
| Odovacar | ||
| Ödön | (Odön von Horváth, austrian writer) | |
| Odran | (irish, version of Odhrán) | |
| Odysseus | (greek) | |
| Oeneos | (greek) | |
| Oengus | ||
| Ofer | ||
| Ofir | (scriptural) | |
| Oginga | ||
| Ogo | ||
| Ogosdinos | ||
| Ogust | (see August) | |
| Ohad | (scriptural) | |
| Ohan | ||
| Ohanis | ||
| Ohannes | ||
| Ohl | ||
| Oijid | ||
| Oisin | (irish, transcriptional version) | |
| Oisín | (irish) | |
| Øivin | ||
| Okan | ||
| Oket | ||
| Okey | ||
| Okou | ||
| Oktaw | (perhaps the polish short for Oktawianusz etc.) | |
| Oktawian | (polish, see Octavianus) | |
| Oktawianusz | (polish, see Octavianus) | |
| Okwonkwo | (african) | |
| Okwui | ||
| Ola | ||
| Olachi | ||
| Olaf | (scandinavian) | |
| Olaff | (see Olaf) | |
| Olafur | ||
| Olajowon | (nigerian) | |
| Olajuan | (nigerian) | |
| Olajuwan | (nigerian) | |
| Olajuwon | (nigerian) | |
| Olando | ||
| Olaniyi | ||
| Olaoyé | ||
| Olarewaju | ||
| Olaus | ||
| Olawale | ||
| Olav | (version of Olaf) | |
| Olave | (version of Olaf) | |
| Olavi | (version of Olaf) | |
| Olavus | (version of Olaf) | |
| Olay | ||
| Oldrich | (czech) | |
| Ole | ||
| Olech | (see Alexander) | |
| Olef | ||
| Oleg | (see Alexander) | |
| Oleh | ||
| Olek | (see Alexander) | |
| Oleks | ||
| Oleksand | (see Alexander) | |
| Oleksande | (see Alexander) | |
| Oleksander | (slavian version of Alexander) | |
| Oleksandr | (see Alexander) | |
| Olen | ||
| Oles | ||
| Olier | ||
| Olin | ||
| Oliver | (french) | |
| Olivier | (french) | |
| Olivir | (version of Oliver) | |
| Olle | ||
| Olli | (short of Oliver, female too) | |
| Ollie | (see Olli, version) | |
| Olo | ||
| Olof | (see Olaf) | (Olof Palme, swedish politican) |
| Olov | (see Olaf) | |
| Oluf | (see Olaf) | |
| Oluff | (see Olaf) | |
| Olugbenga | ||
| Olujimi | (yoruba-language) | |
| Olumide | (yoruba-language) | |
| Olusegun | ||
| Olusola | ||
| Olvin | ||
| Olyn | ||
| Omar | (see also Homer and Omer) | |
| Omari | ||
| Omer | ||
| Omero | (italian) | |
| On | ||
| Ondre | ||
| Ondrej | (slovak?) | |
| Onelio | ||
| Onésime | ||
| Ongombo | ||
| Onnig | ||
| Onnist | ||
| Onno | ||
| Onofredo | (italian) | |
| Onofrio | (italian) | |
| Onorato | ||
| Ontarus | ||
| Onufry | ||
| Onuis | ||
| Onuphrius | ||
| Ophrah | (hebrew, also female!) | |
| Oppius | (roman) | |
| Ora | ||
| Oral | (could be a problem, even it only means something like "from the mouth", it is also a naming for a sort of sexual intercourse, check your language deeply first) |
|
| Oran | (irish, version of Odhrán) | |
| Orazio | (italian) | |
| Orbán | ||
| Orbra | (also female) | |
| Orel | ||
| Oren | ||
| Orest | (greek, modernized version) | |
| Orestes | (greek) | |
| Orhan | ||
| Oriata | (sounds female) | |
| Orie | (problematic?) | |
| Orien | ||
| Orin | ||
| Orion | (greek) | |
| Oris | ||
| Orlan | (spanish) | |
| Orland | (spanish) | |
| Orlando | (italian, spanish) | |
| Orlandus | (spanish) | |
| Orlo | ||
| Orlondo | ||
| Orlondon | ||
| Ormond | ||
| Ornette | (due to the ending on "ette" it could be seen female as for example Annette) | (Ornette Coleman, american jazz-musican [*1930]) |
| Orrin | ||
| Orseas | (greek) | |
| Orson | (french) | |
| Orval | ||
| Orville | ||
| Osama | (see also Oussama) | |
| Osbaldo | ||
| Osbert | ||
| Osborne | ||
| Oscar | (norwegian) | |
| Osdag | ||
| Oshin | ||
| Osip | (see Joseph) | |
| Oskar | ||
| Oskarek | ||
| Oskari | (finnish version) | |
| Osman | (by- or surname of first turkish kings) | |
| Osmane | ||
| Osmanek | ||
| Osmo | ||
| Osmond | ||
| Osseynou | ||
| Ossi | ||
| Ossian | ||
| Ossip | (version of Joseph) | |
| Osvaldo | (spanish or italian) | |
| Oswald | ||
| Oswiu | ||
| Oszkar | ||
| Ota | (czech) | |
| Otfrid | ||
| Otfried | ||
| Otgar | ||
| Otger | ||
| Othilulf | ||
| Othmane | (see Osman) | |
| Othmar | ||
| Otho | (often a transcription version of Otto, most if transcripted into french) | |
| Otik | ||
| Otis | ||
| Otman | (see Osman) | |
| Otnant | (medieval) | |
| Otniel | (scriptural) | |
| Oto | (see Otto and Odo) | |
| Oton | ||
| Otokar | (version of Ottokar) | |
| Otta | (czech, version of Ota) | |
| Ottaviano | (italian) | |
| Ottavio | (italian) | |
| Ottfried | ||
| Ottheinrich | ||
| Ottis | ||
| Ottmar | ||
| Otto | (Otto der Große, german medieval king [936-973]) | |
| Ottokar | ||
| Otton | ||
| Oualid | ||
| Oudoa | ||
| Ougo | ||
| Oumar | (see Omar) | |
| Ounan | ||
| Ousmane | (see Osman) | |
| Oussama | ||
| Oussine | ||
| Owen | (hebrew origin, english used) | |
| Ovagem | ||
| Ovagim | ||
| Ovan | (see Owen) | |
| Ove | ||
| Oven | (see Owen) | |
| Ovid | (roman, germanized version) | |
| Ovidio | (version of roman origin) | |
| Ovidiu | (romanian version) | |
| Ovidius | (roman, origin) | (Ovidius Publius Naso - Ovid, roman writer) |
| Ozek | ||
| Ozias | ||
| Oziasz | ||
| Ozzy |