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.

Fueled by the Orange Light of Avarice, the Orange Lantern Corps is dominated by Larfleeze, who jealously guards his power against all others. The rest of the corps is populated by the stolen essences of other beings given form as avatars through the orange light.

An orchestra who intend to perform a composition of music which will bring about the Apocalypse.

Orchis is an organization dedicated to a response to a "Doomsday" scenario involved an extinction-level population of Homo superior. Formed from the ranks of S.H.I.E.L.D., S.T.R.I.K.E., S.W.O.R.D., A.R.M.O.R., A.I.M., Alpha Flight, H.A.M.M.E.R. and HYDRA,

Popularized by J. R. R. Tolkien, the Orcs have gained widespread popularity and can be found in most fantasy literature.

The Order were the California state intiative super-team.

The Order of Ancient Mysteries was a Mystical Organization.

A religious group that splintered from the Order of Saint Dumas.

Originally a splinter group from the Knights Templar, the Order of St. Dumas created a series of superhuman champions named after Azrael, the angel of Death.

A group of priests and knights formed to fight Shadows.

A secret sect of the Roman Catholic Church which fought against the Black Angel Exael and his demonic minions. A notable member of the team is Sister Mary.

A team that fought Cecil Stedman.

A cult that worships Mistress Death. They sacrifice half of their order to summon Death's physical aspect.

An order of ancient vampire hunters.

A secretive fraternity started by a mutant seeking redemption for past sins.

A group of terrorists who plotted world takeover. They invested in Walter Lawson, and subsequently killed him and subsequently targetted Captain Marvel who was impersonated the deceased Lawson.

Space pirates that steal organs and sell them to those in need

A race of warrior women who live in the Mirror World.

A group of people, orphans, who have lost their families, friends and children at the hands of the Wolverines, and vow to seek revenge against them.