The people of Oerth worship many gods, but after a major war, patterns of allegiance change. The focus in this article is on the gods of the central Flanaess; those that are exclusively worshipped by the monstrous races, for example, are too distant from the lives of most Flanaess folk to be considered here.
The Gods' Relationship with Mortals
The Powers of Oerth rarely intercede directly in the affairs of Oerth. They expect their servants to be their right (and left) hands in the world. Clerics, priests, paladins, and less exalted but still valued souls are the agents of Powers, however minor their deeds may be. The Powers have an implicit understanding that if one of them should act too directly, others will act in concert to oppose the meddler, for if all acted in such a manner, Oerth would be destroyed by the Powers.
This helps us understand why Iuz has been able to effect so much evil in the Flanaess. The Prime Material is his home plane, and therefore, he has a direct involvement in its affairs that other Powers do not. The servants must oppose Iuz, not the Powers themselves. One partial exception to this is St. Cuthbert of the Cudgel, a power devoted to the cause of law. Other Powers allow St. Cuthbert to act in limited ways to oppose Iuz. Why they do this, and how far St. Cuthbert is allowed to act, is a matter known only to the Powers.
In other respects, the Powers regard mortals as they do in almost all worlds. Mortals give reverence and their clerics and priests receive spells. The Powers watch with varying degrees of involvement. Greater Powers tend to have less involvement than Lesser Powers, because Greater Powers are more absorbed in the affairs of many worlds and transcendent events that are far beyond the affairs of mortals.
Mortals' Relationship with the Gods
Mortals regard Powers as they do in most worlds: with reverence, awe, fear, attempts at placation, and so on. In the Flanaess, however, special factors are at work after the wars. The following is true for the non-evil lands of the central Flanaess:
First, there is a general increase in prayer, reverence, and all forms of devotion to Powers. In uncertain times, mortals turn to the great ones for protection and reassurance. Clerics and priests are widely respected and are given more offerings by even the poorest of their flocks. General superstitiousness is a byproduct of all this.
Second, there are changes in patterns of worship. Mortals most often revere Powers who have everyday affairs of mortals as central concerns—deities of nature, children, health, community, and the like are more widely revered than those of philosophy, arcane knowledge, and ethics. But on Oerth, Powers of war, healing, protection, strength, endurance, and revenge are increasingly turned to for assistance. Many people who before the war would have given small offerings to the goddess Beory (nature, Oerth Mother) or Rao (peace and serenity) now turn to a deity such as Trithereon (liberty and retribution), Heironeous (justice and valor), or the rising cult of Mayaheine (protection and endurance) instead. There is also an increasing tendency to appease, if not actually revere, deities of fate such as Istus, and deities of luck such as Ralishaz. Of course, this is less true of wise folk and specialists who might revere a Power of magic, metalworking, or similar niche.
Demihumans are another matter, although deities such as Clangeddin Silverbeard, the Dwarven god of battle, have not lost followers in times of conflict. Arvoreen the Halfling defender Power receives many offerings and prayers these days.
Powers of Humankind
Deities are divided into four groups: greater, intermediate, lesser, and demipowers. The basis of this broad distinction is as follows:
Greater Powers: These are distant Powers, far removed from most mortal affairs. Some may be held to be among the Creator Powers of the multiverse or of Oerth. They typically have many spheres of concern, or are absolute masters of just one sphere.
Intermediate Powers: While lacking the great creative force of Greater Powers, they are still very powerful and hold major sway over one or two spheres of concern. In some nations, they may be held as patron Powers, even above a Greater Power.
Lesser Power. A lesser Power may serve greater ones as a messenger or aide, may be a cast-out or solitary Power, or may hold sway over a very narrow sphere of concern. Some Lesser Powers may be declining from exalted status or may be ascending to greater force.
Demipowers: These are the least powerful and are in many ways similar to Lesser Powers. Some may be mortals who have undergone divine ascension (Zagig and Mayaheine being prime examples). Some may even be referred to as Hero Powers.
Various gods of Greyhawk and their symbols.
Dating back to the Great Migration of human races to the Flanaess a millennia ago, the human pantheon is a blend of gods of Baklunish, Oeridian, Flan, and Suel origin, along with a number of gods considered "common" because they are prevelant in most areas regardless of their history of ethnic settlement. At their core the Suel gods tend to be elemental in nature, the Oeridians worship gods of travel and the sky, and the Baklunish worship a mixture of mystical and pragmatic deities, coming together to form what is a diverse and vast pantheon of gods.
The Seldarine is the pantheon of the elves, based primarily in the plane of Arborea.
Tel'Seldarine, as their pantheon is known in Elvish, roughly translates as "the fellowship of brothers and sisters of the wood." The Seldarine are led by the greater deity Corellon Larethian, god of magic, arts, and warfare. According to their myth, the elves were born from the blood of Corellon Larethain and in some versions of this story this blood was spilled when Corellon banished a god from the sunlit realms after they had betrayed him.
The Dwarven pantheon and its tenets are simple and strong, staying with the teachings of their creator deity. The Dwarves believe themselves to be the creations of the greater power Moradin, whom they often credit with creating the world and even all the other gods of every race. The Dwarven pantheon is mostly male and notably lawful, though Dwarves do show deference to gods of other races whose views align with their own, such as Ulaa the human god of hills, mountains, and gemstones.
Consisting of the Gnomish gods that reside on the plane of the Golden Hills and Urdlen, the Gnomish pantheon is referred to collectively as The Lords of the Golden Hills. This pantheon is led by Garl Glittergold, god of Luck and Trickery. Very uniquely among the more civilized races, Gnomish religious practice is very secular, with Gnomes not even having a creation myth. Gnomes view their deities less as all-powerful beings far removed from the world and see them more as friends and mentors.
The Halfling pantheon is normally small, though it has many gods representing villages, forests, rivers, lakes, beloved ancestors, and so on. Led by Yondala, goddess of protection, wisdom, and fertility, Halflings often refer to both themselves and their pantheon as "Yondalla's Children". As evidenced by the number of gods they have versus the number each individual actively worships, Halflings view religion as a very personal matter. As such have a number of different creation myths they believe, some even believing Yondalla discovered the Halfling race and adopted them as her own.