Beltar, a Suel goddess of Oerth, is a lesser deity, patron of deep caves, pits, and malice. She is chaotic evil in alignment, with chaotic neutral tendencies. She appears in many forms, including a beholder, a red dragon, a withered crone, and a Marilith. Her Realm is in Carceri.
She was once goddess of mines and earth, but was supplanted by other deities, including Moradin, Garl Glittergold, Jascar (who took the form of a winged horse while he battled her), and Fortubo. She is mostly worshiped by savage humans and subterranean nonhumans. She hates most everything.
Sources: Complete Divine, Dragon magazine #89 - "Gods of the Suel Pantheon",
http://www.wizards.com/rpga/downloads/LG_Deities.zip, Living Greyhawk Gazetteer, Living Greyhawk Journal no. 3 - "Gods of Oerth", Player's Guide to Greyhawk, The Scarlet Brotherhood, The Temple of Elemental Evil
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