The Multiverse is a term used by Portal Corporation and various other organizations to refer to the infinite possibilities of alternate universes.
- Primal Earth: Home of the Freedom Phalanx and Arachnos, along with all non-Praetorian player characters. Most of the game takes place here. Primal Earth's main unique feature is that it was involved in an interdimensional war with Rikti Earth, resulting in the destruction of most of Paragon City. War Walls using captured Rikti technology protect the undestroyed City Zones, where Paragon's citizens live, and pen in destroyed Hazard Zones, where only heroes are allowed. Additionaly, Mediporters, also developed from captured Rikti technology, have made hero combat deaths almost non-existent by swiftly teleporting injured heroes away and healing them.
- Praetorian Earth: Home of the Praetorians. Many prominent heroes and villains from Primal Earth have alternate versions that exist in Praetoria, although they are often of a very different moral character. Most of Praetorian Earth has been conquered by Hamidon and its Devouring Earth monsters. The remaining human population is controlled by Emperor Marcus Cole, Tyrant, from his city of Praetoria, which was built upon the ruins of Paragon. Cole's regime is opposed by the Resistance and Praetoria's version of the Carnival of Shadows, called the Carnival of Light.
- Rikti Earth: Home of the Rikti. Rikti Earth destroyed magic and gods early in its history and was visited by an unknown alien power around the time of 2000 B.C. The Rikti are genetically similar to humans but were altered by the aliens that visited them into having a "Hive Mind".
- The Shadow Shard: Mysterious realm that defies normal rules of reality and is home to Rularuu the Ravager after the heroes of Earth Prime banished him there, ending his devouring of universes. Humans do live here, but most have been evacuated to Earth Prime.
- Warrior Earth
- Zeta Tao 7-63 (Shadow World)
- Black Swan's dimension and one of 17 Shadow Worlds. She gets her power and her Shadow minions from this dimension.
- Alpha Upsilon 24-2
- A world destroyed by your alternate self, now inhabited by Ghosts resentful of the living.
- Omicron Zeta 12-20
- Epsilon Tau 27-2
- Hydra dimension
- Omega Omicron 26-20 (Council Empire)
- A world controlled by the Council Empire.
- Tau Gamma 9-24
- Delta Zeta 24-10 (Axis America)
- Homeworld of the Reichsman. World where Nazi Germany won World War II.
- Abandoned world
- A world currently overrun by the Devouring Earth after 70% of the world's population was destroyed by Primal Earth's Nemesis's doomsday device. Targeted by Nemesis because the planet's population was mostly dark-skinned.
- Sigma Psi 20-7
- Tau Delta 8-7
- Nemesis Automatons World
- Nu Beta 9-7
- Lamda Rho 57-20 (Werewolf World)
- Gamma Upsilon 28-3
- A world controlled by Nemesis, who is opposed by a secret cadre of freedom fighters.
- Multiple other Nemesis controlled worlds
- A world in which the hero must venture into to save several scientists' other halves.
- A world in which Nemesis was able to take over by blocking out the sun with self replicating smog machines.
- A world in which Nemesis took over by hooking the population on Superadine.
- Circle of Thorns world
- The hero must travel here to locate a copy of the Tome of Persephone.
- A world nearly overtaken by the Devouring Earth
- Another abandoned world
- A "dead world"
- A "static" world
- Rho Mu 7-2
- Rho Mu 7-3
The portions of the older Story Bible that were released contain much more detail about the nature of the multiverse than the game itself. The section on Rularuu the Ravager gives a description, but it is unknown if this description remains valid for missions written after its release.