Obelix

Oborus-Slither

Obsianus Golem

Odin (Final Fantasy)

Oddjob

Ogre (Tekken)

Ogre Enforcer

Olaf (Lost Vikings)

Olvan Jaess (Seventh Saga)

Omega/Omega Weapon

Omega Red

Ophelia

Optimus Primal (Beast Wars Transformers)

Orion (Bomberman)

Overdrive

Ovnunu

Ox (BOF)