King Bad Ass
Halaster Blackcloak is known as the infamous and powerful Mad Mage of Undermountain. Within the game world, Halastar arrived with his seven apprentices to make his lair in an old abandoned dwarf fortress long ago, before Waterdeep existed. A wizard of undeniable prowess, he soon transformed the ancient caves into a fearsome dungeon, in fact the rumored deadliest and certainly most renowned of all Faerun by “collecting” a huge number of extraplanar monsters and installing numerous traps and portals. Using his magical talents, he turned Undermountain into a quasi-mythal, gaining powerful abilities and immortality within his complex. The drawback, however, was this turned him also completely mad while he was in his dungeon.
The Dungeons & Dragons supplement Expedition to Undermountain states that Halaster died trying to prevent an unknown magical threat dwelling (or fated to dwell) in Undermountain. Remnants of his spirit haunt his old lair, not a ghost but rather memories.