Maglubiyet, the Mighty One, Lord of Depths and Darkness, is the chief god of both goblins and hobgoblins. He urges his worshipers to expand their numbers and overwhelm their competition. His Petitioners war endlessly against the petitioners of Gruumsh.
Maglubiyet is a jealous deity, permitting his servants to rise no higher than lesser deities in status. He killed two of his own sons who he felt threatened his power, sending them on suicide missions against the orcs and dwarves.
Maglubiyet dwells in Clangor, the goblin realm, is in Avalas, the first Layer of Acheron, with the lesser goblinoid gods Nomog-Geaya and Khurgorbaeyag. Clangor is a dusty, flat desert whose cities rise with mathematical precision, but the goblins also tunnel deep within the surface of the cube. Maglubiyet is said to dwell at the bottom of a plummeting waterfall in the River Lorfang, sitting on a throne of flame.
Maglubiyet appears as a huge, black-skinned goblin with red flames for eyes, sharp fangs and clawed hands. His symbol is a bloody axe.
Sources: Monster Manual (3rd edition), Complete Divine, Defenders of the Faith, Deities & Demigods (First Edition), http://www.wizards.com/rpga/downloads/LG_Deities.zip, Monster Mythology, Manual of the Planes (1st and 3rd edition), On Hallowed Ground, Player's Guide to Faerun, The Great Modron March, Planes of Law