Obsidian (2000 - Beast Machines)
Obsidian (2002 - RiD)
Obsidian (2003 - Universe)
Oceanglide (2003 - Armada Sea Mini-Con Team - maroon)
Oceanglide (2003 - Armada Sea Mini-Con Team - blue)
Octane (1986 - G1 Triple-changer)
Octopunch (1989 - G1 Pretender)
Off Road Patrol (1989 - G1 Micromaster)
Offshoot (2004 - Energon)
Oiler (1990 - G1 Micromaster Metro Squad)
Omega Prime (2001 - RiD)
Omega Prime (2003 - Universe - Sam's Club)
Omega Spreem (1991 - G1 Action Master Elite - Europe)
Omega Supreme (1985 - G1)
Omega Supreme (2004 - HoC)
Omega Supreme (2004 - Energon)
Onslaught (1986 - G1 Combaticon)
Onslaught (1994 - G2 Combaticon)
Onyx Primal (1996 - BotCon)
Optimal Optimus (1998 - Beast Machines)
Optimus Minor (1999 - Transmetal 2)
Optimus Primal (1995 - Beast Wars - bat)
Optimus Primal (1996 - Beast Wars - gorilla)
Optimus Primal (1997 - Transmetal)
Optimus Primal (2000 - Beast Machines)
Optimus Primal (2000 - Happy Meal)
Optimus Primal (2001 - Blast Punch)
Optimus Primal (2002 - RiD Air Attack)
Optimus Primal (2003 - Universe)
Optimus Prime (1984 - G1)
Optimus Prime (1988 - G1 Powermaster)
Optimus Prime (1990 - G1 Action Master)
Optimus Prime (1992 - G2)
Optimus Prime (1994 - G2 Hero)
Optimus Prime (1995 - G2 Laser)
Optimus Prime (1995 - G2 Go-Bot)
Optimus Prime (1997 - Machine Wars)
Optimus Prime (2001 - RiD)
Optimus Prime (2001 - HoC w/ Axe)
Optimus Prime (2001 - HoC Spark)
Optimus Prime (2001 - HoC w/ Apex Armor)
Optimus Prime (2001 - HoC)
Optimus Prime (2002 - CS I)
Optimus Prime (2002 - CS II)
Optimus Prime (2002 - Happy Meal)
Optimus Prime (2002 - Armada)
Optimus Prime (2002 - Armada Super-Con)
Optimus Prime (2002 - RiD Spychanger)
Optimus Prime (2003 - Armada Powerlinx)
Optimus Prime (2003 - Armada giftset)
Optimus Prime (2003 - Universe - Sam's Club)
Optimus Prime (2003 - WSTF - Japan)
Optimus Prime (2004 - WSTF anime - Japan)
Optimus Prime (2004 - WSTF white - Japan)
Optimus Prime (2004 - 20th Anniversary Edition)
Optimus Prime (2004 - Spychanger)
Optimus Prime (2004 - Universe Spychanger)
Optimus Prime (2004 - Energon)
Optimus Prime (2004 - Energon TRU Exclusive)
Optimus Prime (2004 - HoC w/ Communicator)
Orcanoch (1997 - Beast Wars Microverse)
Outback (1986 - G1)
Oval (2002 - Armada Street Speed Mini-Con Team)
Overbite (1988 - G1 Seacon)
Overbite (2004 - Universe)
Overcast (2005 - Energon)
Overdrive (1985 - G1 Omnibot)
Overflow (1990 - G1 Micromaster Battlefield HQ)
Overkill (1987 - G1)
Overload (1989 - G1 Micromaster)
Overload (2003 - Armada)
Overlord (1988 - G1 Godmaster - Japan)
Override (1988 - G1 Triggerbot)
Override (2005 - Cybertron)
Override GTS (2006 - Cybertron)
Over-Run (1990 - G1 Action Master)
Over-Run (2002 - Armada Mini-Con)
Over-Run (2004 - Universe Mini-Con)
Ox (2000 - Car Robots - Japan)
Ox (Jusco/clear) (2000 - Car Robots - Japan)