Obliterator
Oblivion
Obnoxio the Clown

Gender: ♂
Universe/Dimension/Timeline: Whattheverse

Main
Crazy (III) 1
Crazy TPB 1
What the -- ?! 13, 24

Michael O'Brien
Obscurity Legion
Observer-X
Occult
Occulus
Dr. Jeannine O'Connell

Gender: ♀

Ocsh the Darkhawk ship
Otto Octavius (HouseOfM)

Gender: ♂
Alternate version of: Doctor Octopus (Otto Gunther Octavius)
Universe/Dimension/Timeline: Earth House of M

Octessence
Oddball (Elton Healy)
Oddball (Orville Bock)

Orville Bock
Gender: ♂
Member of: Death-Throws

Odin
Odin (Earth MiniM)

Odin
Gender: ♂
Alternate version of: Odin
Universe/Dimension/Timeline: Earth Mini Marvels

Features
Black Widow (I) 3.FT
Giant Size Mini-Marvels: Starring Spidey 1.FT

O'Donnel

O'Donnel
Gender: ♂
Owner(s) of: Princess Bar

Features
Wolverine Encyclopedia 2.FT

Odotopians

(Odotopians)
Subgroup of: Alien Races

Offenders
Officer O'Krime
Offset

Gender: ♂
Member of: Shi'ar Death Commandos

Ogor
Ogre
Ogu
Ogun
Jake Oh

Gender: ♂

Features
Iron Manual Mark 3 1.FT

Young Miguel O'Hara (Young)
Ohyaku

Gender: ♂

Features
Heroic Age: Villains 1.FT

Idie Okonkwo

Gender: ♀
Alias: Oya
Member of: Five Lights

Features
Heroic Age: X-Men 1.FT

Okoye

Gender: ♀
Inhabitant of: Wakanda
Member of: Dora Milaje

Ol' Flame Head
Old Lace
Old Man Logan
Old Man Punisher

Frank Castle
Gender: ♂
Alternate version of: Punisher (Frank Castle)

Main
Old Man Logan Annual 1

Old Man Spider

Gender: ♂
Universe/Dimension/Timeline: Earth-94

Main
Spider-Verse (HC) 1
Spider-Verse Team-Up 1
Spider-Verse TPB 1

Old Skull
Old Soldier (Earth SupPow)

Gender: ♂
Universe/Dimension/Timeline: Earth Supreme Power (Earth-31916)

Support
Squadron Supreme (III) 11

Olivier
Olympia
Olympus
Alfie O'Meagan
Omega
Omega Core
Omega Flight (I)
Omega Flight (II)
Omega Gang
Omega Red
Omega Red (Ultimate)

Universe/Dimension/Timeline: Earth Ultimate (Earth-1610)

Features
Ultimate Secrets 1.FT

Omega Sentinel
Omega the Ultimate Alpha

Gender: ♂
Individual of: Alpha Primitives

Omega the Unknown
Omegex

Omegex

Features
Hulk (III) 50.FT

Omniverse
O*N*E
One Above All
O*N*E Sentinels
One-Eyed Jacquie

Gender: ♀
Member of: G.R.A.M.P.A.

Oneg the Prober
Alan O'Neil
Onionhead
Onslaught
Onyxx

Sidney Green
Gender: ♂
Individual of: Mutants
Student(s) at/of: Xavier Institute for Higher Learning

Features
X-Men Earth's Mutant Heroes 1.FT

Oog
Opal

Gender: ♀

Features
Marvel Swimsuit Special 1.FT

Opal Lun Sat-Yr9

Opal Luna Saturnyne
Gender: ♀
Alias of: Saturnyne
Universe/Dimension/Timeline: Unknown Universe/Dimension/Timeline

Operation: Lightning Storm
Operation: Rebirth
Operative

Dennis Piper
Gender: ♂
Member of: Mystery Men

Oracle