The Ashmadai were a secretive devil worshiping cult based in Neverwinter dedicated to the god Asmodeus. The cult was well connected in Neverwinter prior to the cataclysm in 1451 DR and was even better connected as of 1479 DR. In the years prior to Neverwinter's destruction, the Ashmadai worked as agents of Thay although since the cataclysm, the Ashmadai are no longer allied with Szass Tam.
The Ashmadai had the ability to summon devils. However, whenever they summoned a fiend, they bound its essence to the body of a mortal. Because of this the Asmadai kidnapped residents of Neverwinter in order to make them vessels for summoned devils.
Years before the cataclysm of Neverwinter, cultists of Asmodeus allied themselves with Thay. The exact nature of the bargain between the cult and Szass Tam was unclear, what was known was that Thay's regent, Valindra Shadowmantle, possessed a staff that the Ashmadai considered precious. The Ashmadai served Thay loyally, though all they simply desired was the staff. When control would be given to Sylora Salm, the Ashmadai would continue to serve loyally. After destroying Neverwinter to create a Dread Ring, the Ashmadai would again attempt to wreak havoc with Salm by trying to use the primordial of Gauntlgrym to destroy New Neverwinter. But the interruptions of Drizzt Do'Urden would result in the death of Salm and the transferring of leadership to Valindra Shadowmantle, under whom the loyalty would waver. The cultists would stick with Valindra when she would show her possession of the staff, and though they had not seen it since, they assumed her to still have it. Though in reality, Szass Tam had reclaimed the staff.
As of 1479 DR, the Ashmadai now ran in two groups, one slavishly loyal to Asmodeus, this faction was led by the dwarf Favria. His faction consisted of older and less studied cultists who still served Thay in belief Valindra was the staff's holder. This sect was little more than thugs and brutes loyal only to Asmodeus and Favria.
The other sect, led by Mordai Vell, was populated by cunning and manipulative individuals who care more about the acquisition of power rather than paying homage to it. Vell has been credited for bringing about the rise of the Ashmadai into New Neverwinter's shady and secretive powerhouse. Although Vell's sect still pay's lip service to Thay, it advances plots of it's own. Vell, once he gains Valindra's phylactery or the staff, plans to move against Thay.
However, as Vell lacked the numbers and individual power to control Neverember, he used a pod system to shroud the Ashmadai from the eyes of others. The highest ranking members of the sect were unaware of each other and each reported only to Vell. Each of those members had their own pod, and the members of that pod reported to that individual and so on down through the ranks. Mordai readily encouraged his followers to mark shellacked buildings and corpses with the symbol of Asmodeus. This was to intimidate others into joining the ranks of the Ashmadai. The symbol was effective as it managed to scare the townsfolk into co-operating with the demands of the Ashmadai. Although Favria disagreed with the plan, she did not deny it's effectiveness.
A huge part of the Thay-Shadovar War was the conflict between the Ashmadai and the Abolethic Sovereignty. Mordai was determined to make sure that the Aboleths made no advances in New Neverwinter. To do this, Mordai wanted to undermine the Chasm in southeast Neverwinter, a place of interest to the Sovereignty. The cultists constantly hampered the Aboleths' attempts to make people mindless slaves, under the belief that all belong to the Ashmadai, and took special note in killing or driving out Abolethic agents. However, the Ashmadai were relatively unsuccessful, thus the Aboleths did not take the Ashmadai as a threat and have not wiped them off the face of New Neverwinter.
The Ashmadai's other dealings in the war were relatively minor. It mainly consisted of planning to dispose of Thay and sporadically working with the Netherese against their former masters.
The Ashmadai tried to corrupt New Neverwinter supporters at every opportunity. Cultists were not able to sway Mayor Soman Galt, so they began focusing on the Mintarn mercenaries instead. Mordai VeIl had his suspicions about Galt, but the sect leader wanted more evidence before he marked the mayor for death. As of 1479 DR, Mordai was working on General Sabine, whom he regularly invited to his estate. Ultimately, the devil-worshipers aimed to corrupt Lord Neverember and send him back to Waterdeep so the Ashmadai could actively run both cities. As for Neverember, he thoroughly enjoyed Mordai's company, and the two spent time together often.
The Ashmadai cultists still payed some fealty to Valindra, at least enough to keep her from seeing the knife they held poised behind her back. Once they recovered the scepter or found her phylactery, they intended to move against the lich.
The devil-worshipers were in awe of the Netherese, whose representatives approached Mordai on several occasions. The cultists could not allow the Thayans to see them in bed with the Netherese, however, so such meetings were kept a close secret.
While the Shadovar Prince Clairburnus saw the Ashmadai as simple lapdogs of the Thayans, other Shadovar do not. The Netherese cleric Orthinos Eln dispatched troops to learn if the Ashmadai were diverging from the Thayans.