They are a duo of private investigator's.

A clandestine A.R.G.U.S. unit dedicated to investigating superhuman and supernatural occurrences and determining how to handle such situations.

Russian gangsters located in Gotham City. They run illegal business with drugs and diamonds.

The Justice League Odyssey is a team formed to bring order to the new space sector known as the Ghost Sector.

The Offenders were assembled from various points in time by The Collector to face off against The Grandmaster's time-displaced Defenders as part of a bet made by the two Elders of the Universe. The Offenders were led by Red Hulk.

The O-Force was a celebrity mutant group, whose exploits where made into a reality series. They where the counterpart to the X-statix team, untill many members died during a mission.

The offspring of the Ogdru Jahad.

O.G.R.E. (Organization for General Revenge and Enslavement) is a subversive organization faced by Aquaman and Mera during the 1960s.

Mythological creatures from European folklore.

The race of celestial beings who preceded the New Gods, and ruled the Third World.

The Gods of the planet Zenn-La refers to the collective group of celestial beings that watched over Zenn-La. Like the gods of Earth, they were divided into several groups and belief systems.

Retired superheroes and sidekicks were recruited in response to the increasing number of teenage superheroes. Their goal was to not allow teenage superheroes to come to harm, mostly Young Justice.

An ancient race of powerful pure-breed demons who ruled the Earth during the Primordium Age.

Thanagarian Marauder group.

World's largest secret intelligence, defense, and counter terrorism agency.

Enemies of Hercules

OMACs (Observational Metahuman Activity Construct/Omni Mind And Community) are cyborg sleeper agents controlled by Brother Eye.

Omega Core are guards stationed at the pan-galactic prison Kyln.

Omega Flight is a Canadian superhero team and follow up to Alpha Flight.

Formed and lead by Kid Omega, the Omega Gang was a group of Charles Xavier's students that questioned Xavier's philosophy and school policies. They are most known for leading a riot at the Mansion.

A group of freedom fighters from the Vega System who oppose the tyrannical rule of the Citadel.

A team of superheroes set up by the government

Omega Team is a special MI-6 squad lead by Morgan Spetz.

Four cosmic entities awakened by the breach of the Source Wall. They feed on the energy of galaxies and are large enough to crush Earth in a fist.

Parody to Marvel's X-Men.

Company which develops new technologies.

A team led by O, the son of Juncture, it is an opposing team to King Squad but largely seeks to fight oppression from people like Theo Mann.

ONE, or officially, the Office of National Emergency, was created to deal with the sudden explosion in the mutant populous.

After the Joker murders Lois Lane and her unborn child, Superman takes it upon himself to begin policing the world, creating a worldwide dictatorship with like-minded superheros and villains, who either joined willingly or were forced to join with the threat of death.

Formed by Darth Krayt, the One Sith believe the Rule of Two used previously by the Sith to be faulty, believing that the idea of the entire Sith Order being "one body" would fend off destruction from within.

Oni are a kind of yokai or demon from Japanese mythology. They are commonly portrayed as ogre-like creatures with claws, wild hair, and horns growing from their heads.

Race that control a mining Planetoid

Onslaught is an extremist sect operating out of Kahndaq and the Republic of Kasnia.

Government task force that takes on supernatural missions

Operation: Knightstrike is a top secret task force composed of enhanced mercenaries led by Chapel.

Ms. Marvel agreed to join his Mighty Avengers team if she would be allowed to operate a small strike squad known as Operation: Lightning Storm that would hunt the worst of the worst of the world's super-villains before they became a problem for the Avengers to deal with.

The Ophidians were Snake-Men who battled man in ancient times.

Infectious parasitic fungus which existed since the beginning of Earth. The Lamia co-opted Poison Ivy in order to drive humanity towards extinction.

A mutant rebel group on Earth-6160

After the Squadron Supreme killed Namor, Nighthawk bought the company.

In the 30th century the Orandans hail from the planet Orando where a medieval feudal system still reigns the land. Not trusting outsiders the royal member called Princess Projectra is a representative in the Legion of Super-Heroes.