- Olin J. EggenCitizenship: United StatesBorn: July 9, 1919
- Oliver LabsCitizenship: GermanyBorn: 1974
- Orlando Antonio NaranjoCitizenship: VenezuelaBorn: June 13, 1951
- Otto HauserCitizenship: SwitzerlandBorn: April 12, 1874
- Ovidiu Horațiu VăduvescuCitizenship: CanadaBorn: 1967
- Ōguchi ShūgyoCitizenship: JapanBorn: May 12, 1864