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- Octomus (see The Master, Villains in Power Rangers Mystic Force)
- Octoroo (see Villains in Power Rangers Samurai)
- Oculous (see Villains in Power Rangers Mystic Force)
- Officer Tate
- Olympius (see Prince Impus/Olympius, Villains in Power Rangers Lightspeed Rescue)
- Omni (see Villains in Power Rangers: S.P.D.)
- Onikage (see Villains in Power Rangers: Wild Force)
- Orbus (see Machine Empire)
Read more about this topic: List Of Power Rangers Characters