Halaster Blackcloak

Halaster, the Mad Mage of Undermountain, is the deranged individual behind most of the traps and horrors found in the great dungeon under Waterdeep. Undermountain is his home, an amusement gallery in which others perform to entertain him. The Mad Mage knows the ever-changing ways of Undermountain as no one else does, for he is the one who controls those changes. He prefers to remain unseen, skulking about invisibly or peering through scrying sensors that resemble wide-open eyes surrounded by sparkling motes of light.
Halaster’s abilities far exceed those of most mortal wizards. His expertise with magic gates allows him to travel far and wide to engage in magical research. He spends much of his time creating gates, moving them around, and casting spells on them. Halaster’s gates connect the different levels of Undermountain, thus enabling him to bring new monsters into the dungeon to replenish those that die or escape. Even as groups of adventurers try to gain decisive control of just a small section of Undermountain’s halls, Halaster constantly alters the dungeon’s perils to thwart them.
Halaster’s true form is that of a tall, gaunt, male human, but he uses magic to take on many other visages and shapes. No matter what form he wears, the Mad Mage giggles and mutters incessantly. Contrary to appearances, however, Halaster is alert and attentive to the activities and preparations of all beings near him. He never willingly enters combat without first casting mage armor and mind blank on himself.