Halaster Blackcloak is a fictional character in the Forgotten Realms, a popular setting of the Dungeons & Dragons role-playing game. In the setting, he is known as the infamous and powerful Mad Mage of Undermountain. 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.