Operative (Dennis Piper)

Gender: ♂
Member of: Mystery Men

Oracle
Orator (Victor Ludwig)

Gender: ♂
Member of: Acolytes

Orb (Drake Shannon)
Orb (II)
Orb of Agamotto
Orbucen
Orcale

Member of: S.H.E.

Ord
Order (I)
Order (II)
Order (CtrEarth2)

Alternate version of: Master Order (MultiV)
Member of: Young Allies (II) (CtrEarth2)
Universe/Dimension/Timeline: Counter-Earth (II)

Organizer (Abner Jonas)
Ori
Origin
Origins Corporation
Orion (Viktor Uvarov)
Orka
Orphan-Maker (Peter)
Orrgo the Unconquerable
Ortlinda

Gender: ♀
Member of: Valkyrior

Elizabeth Osborn
Harold Theopolis Osborn (I)
Harold Theopolis Osborn (II) (Earth-1610)
Harold Theopolis Osborn (III) (Earth-982)

A.K.A.: Harry
Gender: ♂
Alternate version of: Harold Osborn (I)
Child(ren): Norman Osborn Jr. (Earth-982)
Universe/Dimension/Timeline: Earth-982 (M2)

Harold Theopolis Osborn (IV) (Earth-99062)
Norman Osborn Jr. (Earth-982)
Norman Virgil Osborn
Osiris
Other-Earth
Ouranus

A.K.A.: Uranos
Gender: ♂
Individual of: Greek Pantheon
Parent(s): Gaea

Features
Official Handbook of the Marvel Universe A to Z Update 2.FT

Outback (Frederick Myers)

Gender: ♂
Alias of: Boomerang (Frederick Myers)
Member of: Heavy Hitters

Outcast

Gender: ♂
Member of: Lilin

Outcasts
Outer Circle of Enforcers (I)
Outer Circle of Enforcers (II)

Member(s): Vanisher (I)

Outlaw (Inez Temple)
Outlaw Kid
Outlaws
Overdrive
Overlord
Overmind (Grom)
Overrider (Richard Rennselear)

Gender: ♂

Features
Wolverine Encyclopedia 2.FT

Oversword
Ovoids
Owl (Leland Owlsley)
Owl Gang
Ox (Raymond Bloch)
Ox (Ronald Bloch)
Oya (Idie Okonkwo)

Gender: ♀
Alias of: Idie Okonkwo
Member of: Generation Hope

Oyakata
Ozymandias