The original D&D settings usually used Earthly gods from Greek and Norse mythology - it wasn't until the Greyhawk Boxed Set and Forgotten Realms settings that original deities were developed for AD&D. Clerics were assumed to worship "the immortals" in B/X, a nebulous conglomeration of unnamed beings of supreme power. By keeping things ambiguous it allowed anyone to add their own flavor to the campaign.
I favor the more detailed approach of world-specific deities and used this model when I designed Thuin/Sturmgard. There are only a few Great Gods and a plethora of lesser gods and demi-gods. Some of the converted deities would resemble this:
LAWFUL
Talas (creator god, dragon lord of the skies and stars)
Aram (lord of paladins, god of righteous justice)
Arne (god of music, art, bards)
Bok (god of bravery)
Kara (goddess of healing and compassion)
Damon (god of the sun, light, and flame)
Dioclesis (Dolestrian principles of culture)
NEUTRAL
Chithara (earth mother)
Baranduin (beast lord)
Bathys (goddess of the seas)
Tomar (god of knowledge)
Kyndar (god of masculinity)
Nairn (goddess of femininity)
Rom (Romisarian principle of commerce)
Mollah (Algozin principle of freedom)
Xaal (goddess of secrets)
Riddlemaster (lord of balance and trials)
CHAOTIC
Spithre (god of chaos, magic)
Gorgus (lord of undeath)
Djun (god of war)
Vetch (god of insanity, jealousy, and criminal rage)
Nelvanna (Lady Ice, mistress of the frozen north)
Shuva (lady of the night, moon goddess)
There are more gods than this; these are only the few I can remember from the top of my head. The various cultures and demi-human races revere these deities under different names. The "principles" (Dioclesis, Rom, and Mollah) are forces empowered by one or more of the deities or by faith alone. I've always envisioned Mollah as a force empowered by a people's need to be free from oppression, a flaming ethereal giant that smites oppressors. This religion resembles early Christianity under the yoke of Imperial Roman rule. The Diocletian faith is representative of the Holy Roman Empire of Constantinople. The Romisarian faith probably resembles ancient Phoenician principles of commerce and the sacred Bond of the Business Deal.
The cosmology of Sturmgard is as a separate sphere in the multiverse, created by Talas for his own amusement. As such it is separate from the world cosmology of D&D and AD&D to some degree. There are accessways to the elemental planes, the positive material and negative material planes, as well as the Ethereal plane, but only Talas inhabits the border Astral Plane and protects his creations from the Chaos of the outer planes. Demons learned of this separate material plane long ago and tricked a mortal to invite them in. This resulted in the Demon Wars that very nearly ended the world. Since then the world's wizards are sworn to protect the planar boundaries and act as interdimensional border patrolmen, policing the use of magic to ensure that such mistakes never happen again.
Since Spithre ran amok in the early years and then after the Demon Wars, Talas has become more and more restrictive, to the point that magic is now failing. With the banishment of Spithre and the removal of the corruption of the demons the world's residual magical energy is being used up by the various magic-users across the globe. Only by releasing Spithre from his confinement can magic return to Sturmgard. However, doing so may unmake reality since it would prove the creator fallible. One of the main goals for high-level play is to convince Talas to reneg on his banishment of the Lord of Chaos, something that may spark new warfare across the world.
