Nosfentor

Nosfentor is the Shadowlord of Cowardice, and is one of three such beings that represent the opposing aspects of the Principles of Truth, Love, and Courage. Appearing first in Ultima V with its siblings Faulinei and Astaroth, this entity later recurs in Martian Dreams, manifesting within the Avatar's psyche as they sleep.

Description
Nosfentor was created through one of three shards of Mondain's broken Gem of Immortality, after it was splashed with the gore of those Captain Johne slew in the course of his insanity. Awakened by the shedding of blood, the eidolon of Cowardice fast assisted its two brothers in the capture of Britannia's sovereign, Lord British, and thereafter joined in corrupting his regent, Lord Blackthorn.. With Britannia's governance thus disrupted, Nosfentor was free to ravage the eight Cities of Virtue, spreading  terror and despair in its wake.

Eventually, however, Nosfentor fell - after having been drawn to Serpent's Hold by the Avatar's utterance of its name and was there defeated when its native shard was cast into the fires of the Flame of Courage.

Years later, however, within the distant cities of Mars, the Shadowlord reappeared in the midst of the hero's machine-induced dreams, manifesting to test the hero before their metaphysical confrontation with Raxachk. Claiming that altruistic Courage was anathema to the basic instincts of the survival, the shade attempted to convince the Avatar to take solace from pain in cowardice, and confronted the hero with a number of illusionary terrors to try their will. When the hero ultimately passed through Nosfentor's gamut of monsters without balking, the Shadowlord vanished, and has not appeared to the Avatar in any form since.

Trivia

 * Nosfentor identifies as female in her appearance in Martian Dreams, although her gender is not demarcated in Ultima V.