Gargauth

Gargauth (pronounced GAR-goth ), or The Lord Who Watches, was the lawful evil demigod of betrayal, cruelty, political corruption and powerbrokers. He embodied the inevitable decay and corruption that accompanied all self-serving, greedy, and power-hungry leaders and groups. Gargauth held to the letter of any agreement, not the spirit, and relished betraying anyone with whom he forged a pact by twisting the contract to serve his own ends.

Worshippers
The church of Gargauth was a secretive faith, although there were some significant exceptions. Clerics worked to increase their personal power, the power of the church, and by extension, the power of Gargauth; they were expected to be Gargauth's eyes and ears throughout Faerûn. They were to entice and corrupt powerful individuals and leaders in communities throughout Faerûn and bind them into strict contracts favorable to Gargauth's goals. They sought to seize positions of power whenever possible and integrated their positions into the secretive hierarchy of the faith. Gargauth directed his followers to undermine other evil faiths and steal their worshipers rather than waste energy in conflicts with good deities. Clerics of Gargauth prayed for their spells at dusk, when night first began to corrupt the day. Gargauth's clergy marked all agreements with signed contracts consecrated in the name of the Lord Who Watches. Many clerics multi-classed as divine disciples or sorcerers.

Holy Days
This occurred each Midwinter night. This horrific ceremony, believed to involve many gruesome sacrifices, heralded the imminent time when Gargauth would seize Faerûn as his unholy kingdom and transport it to Baator to form the Tenth Pit of Hell.
 * The Unveiling :

This was celebrated on the eve of the Feast of the Moon. It was a personal ritual in which each cleric renewed his eternal contract with Gargauth, trading absolute fealty for increased power. This unholy ritual was believed to involve personal sacrifices of money, magic, and hoarded knowledge and the casting of many horrific spells.
 * The Binding :

Relationships
Gargauth was opposed to evil deities such as Cyric and Shar. He posed a particular threat to Siamorphe, given his interest in corrupting those who she held up as shining paragons of virtue.

Gargauth sometimes employed a powerful blue dragon named Rathguul as a steed.

History
Gargauth was once the arch-devil Gargoth whose foul nature was too much even for others of his ilk. Exiled forever from the Nine Hells under pain of complete destruction, Gargauth took to wandering the planes, returning time and again to Toril. The only complete record of these journeys exist in a journal he wrote while making them which is kept in Oghma's library. During this time, he had established a cult following on Toril and absorbed the powers of baatezu who had become stranded on that world.

He almost achieved lesser god status when his cult blossomed during the Harpstar Wars but the concerted effort of Bane, Bhaal, Loviatar and Talona crushed his followers to prevent such an occurrence.