Gelf Darkhearth is the gnomish deity of Entropy and Revenge. He was introduced in Races of Stone.
Gelf is Garl Glittergold's brother, and rarely have two brothers been more bitter rivals. Gelf, depicted as a gray-skinned dwarf with a black beard, takes obsessive delight in opposing everything his brother attempts. This compulsion puts Gelf in the tragic position of tearing down the gnome society he loves, just to thwart Garl Glittergold. Gelf isn't evil, but he feels compelled to destroy everything Garl holds dear. Gelf is an angry, sorrowful deity, and he attracts followers of similar temperament. The reason for Gelf's attitude and rivalry with Garl is not not, but it is possibly because they both covet the Gnomish goddess of love Sheyanna Flaxenstrand. Gelf's holy symbol is a black anvil that is splt in two, set against a murky purple background. His favored weapon is the warhammer.
The gnome pantheon of gods consists of the leader Garl Glittergold, as well as Baervan Wildwanderer, Baravar Cloakshadow, Flandal Steelskin, Gaerdal Ironhand, Nebelun, Segojan Earthcaller, and Urdlen (others might be present in specific settings). Gelf Darkhearth, along with the Glutton, Ril Cleverthrush, and Sheyanna Flaxenstrand, were all introduced in Races of Stone.
Would-be clerics of Gelf are individually recruited by senior clerics who sense kindred spirits. Those who follow Gelf are rebels so committed to their cause that they would do anything to defeat the authorities they despise.
Gelf's temples aren't hidden, but they are out of the way and placed so that Gelf's worshipers aren't seen coming and going. Most gnomes know where to find a temple to Gelf (assuming one is nearby), but few can think of a reason to go there.
Gelf's prayers are often wordless ululations--long strings of vowel sounds. To nonbelievers, they sound like gibberish, but the exact order of sounds has meaning to the faithful.
Many of Gelf's rites seek to bestow a curse or ill will on a nonbeliever. Few are known outside the fairly insular circle of Gelf's worshipers--with one exception: Almost every gnome warrior knows the Rite of the Adroit, a brief group ceremony that steels the minds of gnomes to the chaos of war.
If someone has hatched a plot against one of Garl Glittergold's temples -- or against a thriving gnome community -- Gelf Darkhearth is probably behind it. He takes particular glee in using Garl's faithful against him, duping adventurers into doing his bidding.