The Lord of the Lake

In Rezmouth, the inhabitants are very devout and follow the Protector, the Lord of The Lake, Gnjht’ur. They toil away to do its bidding, in hope that it will reward them with their desires.
Atop the Nameless Mountain on Rez Isle, there is an ancient Helstraad Fortress built during the Century of Bloody Tear, circa 1900AC. It was abandoned following the war, and most of its true treasures taken.
Around 4,400AC, during the 2nd Solution of Integration, a Helstraad Arch Wizard, Cailus Blacktooth, or else known as the fabled Wizard Hermit, alone converted the old fortress into a temple of Azuth. He had been part of the Helstraad Cabal in Hel, but following the The Incursion sought to fix the problems whilst the rest of the surviving cabal holed up in Koth, the Eastern Continent.

Using the last of the magic he had available, Blacktooth locked away an Aboleth in the nearby lake. He tricked the Aboleth into thinking that the temple was there to overlook the lake prison and gloat, and that soon others would come seeking to worship Azuth whilst the Aboleth looked on powerlessly.
Soon the Holy Order of Helm and its Soulguard came to Rez Isle, in their nation-wide crusade to demolish all temples other than those dedicated to Helm. The Aboleth felt their approaching presence and mistook them for people coming to worship Azuth. The Aboleth could feel the minds of the zealots, and surmised that it would not be able to enslave any of them without putting itself into an unacceptable degree of danger. Instead, it used some of its limited amount of stored Weave to cloak the Nameless Mountain in a perpetual fog, which only with its permission anyone can penetrate.
The crusade debated the existence of the temple and unable to penetrate the fog, soon left.

The Aboleth never realised it had just saved the temple from destruction and in doing so, ensured its continued captivity.
Since then, the Aboleth has lured weak minded travelers into its bidding, promising them their desires in return, and they call it the Lord of the Lake. Ultimately the village of Rezmouth was built and others came along following hushed whispers of reward from the Lord of the Lake, or also known as the Protector, a perversion of Helm's faith.
On occasions when there is a particularly talented follower, the Lord of the Lake will enslave them into a Chosen – someone who supposedly is worthy to leave Rezmouth and collect their reward - and secretly tasks them to penetrate the Temple of Azuth to see if they can overcome that what binds the Aboleth. Though none of the Chosen have come back, with its telepathic link the Aboleth remembers all the traps and encounters the Chosen have encountered and how to overcome them. It hopes one day to reach the heart of the temple and destroy whatever is holding it in the lake, and with the returning of the Weave, this could soon be a real possibility.