Eldritch
The setting of Eldritch is a comics-inspired occult pastiche, far more superheroes than any other sort of occult fiction.
The Claviger
Analagous to Marvel's "Sorcerer Supreme," the Claviger is the most potent magician. So called because they are the "keeper of the keys" that lead to this realm, it is given to the Claviger to protect the Earthly dimension from extradimensional intrusions, invasions, and other interferences. The Claviger also trains the most worthy and promising of apprentices, whom eventually become the Masters.
When the current Claviger dies, one of the current Masters becomes the next Claviger. Though the Claviger often chooses an heir prior to their death, Masters who believe they are meant to bear the keys may challenge the heir to a magical duel for the mantle. Such challenges become broader and more wide-ranging in cases where the Claviger has not chosen an heir.
The Masters
Where the Claviger defends the Earthly dimension from intrusion by other dimensions, the Masters of the Earthly Realm defend the world from various magical threats and dangers to it. Most Masters oversee a broad geographical area, which is their responsibility to protect. Many Masters seek allies of other Masters and even some of the other occult denizens of the world in their quests to do so. All Masters have been apprentices of the Claviger at one time, although many very old Masters were apprenticed to an archmage who bore the keys before the current Claviger.
Masters are also responsible for seeking out and cultivating those with magical talent in their ward-realm. Such folk often accidentally find their way into the Demimonde, and it is given to Masters to find out if such folk might become magicians in their own right and training those who will (or seeing that they are put into contact with Masters of powers or styles to which such supplicants are already aligned). When the Claviger decides it is time, they perform tests and interviews with the apprentices of all the Masters in the Earthly realm, seeking out those with not only the skill and talent, but the fate to become Masters themselves. Once an apprentice has been tested, if they are not brought into the Claviger's service, they will eventually complete their training with their Master and leave service as one of the Sojourners - magicians of perfectly capable ability who will never touch the mystical keys wielded by the Masters and the Claviger.
The Sojourners
Sojourners are magicians out in the world on their own recognizance. Their goals and purposes are many and varied - some benevolent, some selfish, some even outright evil. A Sojourner has been tested and rejected as apprentice by the Claviger, and ended their apprenticeship with a Master (sometimes affable, sometimes in contention). Many Sojourners are very capable magicians, having studied a broad base of lore, both under a Master and by seeking out such lore in the wider Demimonde afterwards. Some Sojourners even come to rival Masters in their power, although this almost always only happens via pacts with occult entities, many of which are ill-advised for the sorcerer to bind themselves to.
The Demimonde
There is a world halfway between the mortal, everyday world, and the sanity-shattering occultscapes of purest magic and possibility. This place, where those realms touch with delicate appendages the mortal world, is called the Demimonde. It is not a physical place, per se, although some sacred sites, places of extradimensional intrusion, and dominions of shadowy horror do exist as part of it. The denizens of the Demimonde are creatures touched by magic - magicians, certainly, but also their enchanted servants, their spirits and automatons servitors and familiars, the myriad extradimensional entities that have come to reside in the Earthly realm (and those who command or serve them), as well as a host of supernatural creatures and entities out of legend.
