Golarion is a planet created by Paizo Inc in 2007 under its GameMastery imprint in a generic OGL module and 2 months later it became the primary setting for the Pathfinder roleplaying game. Because Pathfinder takes so much from the Cthulhu Mythos, Golarian is heavily affected by Mythos concepts and creatures.
Golarion is a planet of numerous lifeforms, both sentient and non-sentient. A magic heavy world, with sorcerers, witches, and necromancers. There are dozens of sentient species inhabiting the planet. Which includes both native species and those whom have immigrated to the world or unwillingly ended up on the world (e.g. brought to the world by their former masters). Races which include dragons, elves, giants, krakens, lizardmen, merfolk, elementals, serpentmen, kitsune, etc. Humans are one of the primary races, but they did not originate on Golarion. Legends speak of a homeworld called Earth, and the ethnic groups among the humans are reminiscent of those of Earth (e.g. Chinese).
Golarion is part of a solar system that has a number of inhabited worlds, each of which has more than one sentient species, some of them native and others alien. Like Golarion, they are all magic-heavy worlds. Technologically these worlds range from the bronze age level to the Renaissance period, and societies range from cave-dwelling hunter-gatherer cultures to continent spanning bureaucratic empires. There is also sophisticated alien technology (robots, directed energy weapons, etc) which are the remnants of crashed starships or lost alien settlements, and are therefore rare and treated as artifacts.
The Outer Gods and Great Old Ones have servants and followers on Golarion, though they are in the minority. Among these races are Deep Ones and Neothelids. Cults which worship the Old Ones and/or the Dark Tapestry (Outer Gods) are considered blasphemous by most races and therefore suppressed. The planet has a few Great Old Ones, including Orgesh who was born on Golarion, Mhar who is imprisoned in that world, and Yig. Its sorcerers have visited other worlds under the influence of the Old Ones, as well as the Dreamlands within the Dimension of Dreams.