Karsus

Lord Karsus was the Netherese creator and caster of the Karsus's avatar spell that triggered the Fall of Netheril. "The ‘child-who-would-be-a-god,’ ‘the Unmaker of the Weave,’ ‘the Ape who would fly.’"

- Names of Karsus, given by the Tel-quessir, Cormanthyr: Empire of the Elves

Early life
Karsus was born about 3,100 years after the nation's founding, in. He was able to cast his first spell at the age of two, and by the age of twenty-two had become the youngest arcanist to ever create his own floating city.

Gifted with magic, but lacking the necessary discipline that comes with hard work and research, he founded a school of magic on his enclave and encouraged the attendance of radical thinkers and those interested in taboo projects. One of his students, now known only as Lord Shadow, wrote a treatise on the exploration and exploitation of other planes, such as the Plane of Shadow, which garnered initial criticism but was eventually embraced as the key to an infinite source of shadow-creatures as slave laborers as well as a dumping ground for unwanted garbage.

Creation of Karsus's avatar
In, Arthindol the Terraseer appeared before Karsus and stated, "Mystryl was about to face her greatest challenge - one that could alter the perception of magic for all time."

Shouldering the responsibility for preserving his civilization, Karsus finished creating a spell, Karsus's avatar he had been developing for years. This spell would steal the power of a deity and transfer it to the archwizard that cast it. Karsus believed that with the power of a deity at his disposal, he could destroy the Phaerimm and unite his people. Karsus cast the spell in the 3,520th year of Netheril,, and chose Mystryl, the goddess of magic, as his target, feeling that she was the most powerful deity and the most appropriate choice for his purposes. Karsus gained the powers over all magic.

Fall of Netheril
Unfortunately, his choice was a terrible mistake, for one of the responsibilities of the deity of magic was to regulate the flow of magic to and from all beings, spells, and magic items in the world. Lacking the ability to do so properly, magic surged and fluctuated. With her last remaining bit of power, Mystryl sacrificed herself to block Karsus's access to the weave, causing all magic to fail. The flying cities of Netheril plummeted to the earth. The severing of the link also killed Karsus and transformed him into stone, and the last thing he saw was his entire civilization being destroyed because of his actions. This was to be known as Karsus's Folly. The stone form of Karsus eventually landed in a part of the High Forest, now called the Dire Wood. The city of Karse was built around its base.

Final fate
Karsus was never accepted as a petitioner by any god, nor did he go to the Fugue Plane when he died. Instead, his soul was bound to the Material Plane. Those with experience in Pact magic can call up his vestige where he appears as a giant blood red boulder, like the one found in the High Forest where his petrified form landed. Blood burbles up from the top of the stone, trickling down the side facing the summoner, pooling at the base. When he speaks, the pool fountains upwards, its height varying on the volume of his voice. Karsus grants the summoner a boost in magical ability, though he also imparts some of the arrogance he is renowned for. Also, this vestige for some reason has a strange enmity toward Amon.

Legacy
Karsus held a small cult of worshipers who venerated the 'momentary god'. They were mostly based at Karse until its abandonment.

Exposure to heavy magic and Karsus' own proximity also led to the creation of the karsites, a race of people born with an inherent distrust of magic as well as a natural resistance to it.

Appearances
In the game Neverwinter Nights: Shadows of Undrentide the hero meets Karsus in a hell created by a book in the Great Library of the risen Netherese city of Undrentide, which is implied to be Karsus's own city. Karsus was being tormented by devils but the player can choose to redeem him by re-writing the magical tome in which his spirit is imprisoned. Doing so will ensure that Karsus is present to assist during the battle in the Library's final magical tome.