Xanathar resembled a typical beholder, having a large spherical body some 4.5 feet (1.4 meters) in diameter, with ten eyestalks and a large central eye, above a wide fang-filled mouth. His chitinous hide was colored a dark blue-gray and shaded to a dull yellow-orange around his mouth and on his underside. He normally floated 3 feet (0.9 meters) above the ground.
Xanathar greatly enjoyed being a crime lord just under the noses of Waterdeep's Lords and laughed at their claims to have stamped out organized crime. He was confident in his power and his inconspicuousness to the Lords. His main goal was simply to maintain his position.
Xanathar loved luxury and pleasures, and very much enjoyed well-prepared foods (provided by Steeltoe), scented oils, and spiced tobaccos and herbs from the south. His appetite was huge, and included people. When not engaged in crime, he relaxed in a great glass tank of scented water, where he planned his crimes.
Xanathar was devious.
Xanathar was served by his "four councilors". They met with him regularly and in turn dealt with others in the organizations. No one else knew of Xanathar's existence, let alone that he was a beholder.
Shindia Darkeyes, the half-drow thief, was Xanathar's lieutenant and personal favorite. She oversaw blackmail and exortion. She helped Xanathar kill Uthh, but could do nothing to save it from the Eye. Afterward, she served the Eye grudgingly while plotting its downfall.
Slan Thurbel was Xanathar's mercenary leader and hitman, but Xanathar insulted continuously him and, in Slan's words, did not "respect his talents". Glad Xanathar was dead, Slan much preferred the Eye in charge.
Although Xanathar shared his kind's distrust of magical items, he did have specially made an eyestalk ring of proof against detection and location, which he wore on his fifth eyestalk. He wore rings on all his other eyestalks, but these were non-magical jewelry, valued around 350 gp each.
Xanathar laired in a hidden chamber behind a secret door in the sewers below Waterdeep, accessed by a series of trapped passages. The traps were mostly nonlethal, comprising falling cages and nets or pits, in order to catch trespassers. None but Xanathar and his Councilors knew of the lair's existence and the safe route in, and the few who stumbled into it soon met their ends there. The lair was opulently furnished, and held several treasure vaults and libraries.
Through the Xanathar's Thieves Guild, Xanathar controlled most of the crime in Waterdeep. Rather than operate as a true "thieves' guild", and thus risk the attention of the Lords of Waterdeep, he instead worked entirely through freelance thieves via third parties, so that no-one could reveal his whereabouts, identity, or even existence. Xanathar was the major supporter and advocate of the hundreds of small criminal enterprises in Waterdeep. He was amused by the Lords' claims that no thieves' guild existed in Waterdeep.
Xanathar collected much information about the surface world, also via third parties, and used this to make his plans. It was rumored he knew the most about Waterdeep's sewers and their connections to major buildings and to Undermountain. The guild operated heavily in the sewers and Undermountain. His libraries closely tracked the powers and vulnerabilities of Waterdhavian mages. However, all information in these libraries was written by Slink in a cipher.
However, Xanathar's best defense was secrecy, and he would go to great efforts to maintain it. Operatives who wondered who was in charge was targeted for death by Slan's ritual killers. He also engaged in misdirection, with defenses against magical detection on his lair and having his organization function not at all like a real thieves' guild. He was sure the Lords would tear apart the city's sewers to locate his lair, if they but knew of his existence. His other reason for staying anonymous was so his former masters in the Zhentarim could not find him.
Xanathar originally came from the Anaurian Hive.
Xanathar was originally a follower of the eye tyrant Xantriph, who was an ally of Manshoon of Zhentil Keep. Xanathar was sent by the Zhentarim to Waterdeep to plot the downfall of the Lords of Waterdeep and establish a ruler friendly to the Zhents. He arrived hidden in cargo in a trading caravan from Zhentil Keep. However, after lurking around the docks and conspiring for a couple of months, Xanathar was inspired by Waterdeep's free market atmosphere and sensed a power vacuum in the city's underworld. He soon went independent, and vanished from his masters' view. Acting independently, he established a network of thieves who worked for him and located a hideout below the city. He brought many of the disparate freelance criminal operations under his covert leadership.
By the 1350s DR, Xanathar led a great but "unofficial" thieves' guild and only his lieutenants, the "four councilors"—Slan Thurbel, Slink Monteskor, Ott Steeltoes, and Shindia Darkeyes—knew his true nature and aspirations. It was well established by 1357 DR.
However, beginning around 1354 DR, another beholder had set its sights on the Xanathar's Thieves' Guild. Already the leader of a slaving ring based in Skullport, the beholder known as the Eye desired to increase its power and influence by taking over the thieving organization. Over ten years, the Eye studied the Xanathar's Thieves' Guild and questioned charmed people in the know, and found subtle similarities in how their two groups behaved, things only a beholder would recognize. It thus learned the Xanathar was a fellow eye tyrant from a different hive, and plotted to eliminate a rival and seize more power in one swoop. Xanathar remained completely unaware as, over a few years, the Eye's investigations revealed the location of its lair. The Eye kept its own nature secret from Xanathar.
In the mid-1360s DR, Xanathar attempted to organize the disparate thieves of Waterdeep into a new guild. However, the effort was thwarted and Xanathar was defeated by bold adventuring companies commanded by Lord Piergeiron of the Lords of Waterdeep, and was the latest such effort by 1367 DR.
Xanathar's ruin came at last at some unknown time in the late 1360s DR, when the Eye, via its agents, carefully manipulated another Skullport beholder, Uthh, and tricked it into attacking Xanathar in the sewers under Waterdeep. Although Xanathar defeated Uthh, it was left weakened and, taking advantage, the Eye arrived and easily killed Xanathar. Afterward, the Eye replaced it, telling Xanathar's former minions that "the Xanathar" was but a title. Persuaded by charm spells and by death rays at dissenters, most agreed to stay and serve it. The Eye retained most of the original Xanathar's policies and practices; the transition was so smooth that those outside the four councilors remained unaware of the change. "The Xanathar" had taken full control of the Xanathar's Thieves' Guild and gained great power and influence by 1368 DR.
In truth however the original Xanathar was killed in 1358 by an adventuring band under orders of the Lords of Waterdeep and secretly aided by another beholder that assumed the identity of the Xanathar.
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