Shadowlords
The Shadowlords are 3 wraith-like, demonic entities.
There are 3 Shadowlords 1 for each of the anti-principles: Hatred (Astaroth), Falsehood (Faulinei), and Cowardice (Nosfentor). (In opposite to the Principles of Love, Truth, and Courage.)
The Shadowlords embody their respective anti-principles in a manner similar to how the objects of each Principle embodies it.
The Shadowlord of Hatred, Astaroth, was behind attacks on the Shrines associated with Love during the Spring of 2007.
The Shadwolords are part of Ultima lore, but were not actually seen in-game until the Mad Mage event in early Spring 2008. (See Blackrock Detector. A graphic originally attached to them was used for the Harrower.
The Shadowlords bear physical similarities to the Time Lord and the shadowy Traders who "bought" blackrock from characters, thus setting up the destruction of Haven and the establishment of New Haven.
After many years of being referred to, the Shadowlords were finally seen when the "Mad Mage" Kronos unleashed his Blackrock Detector upon the world in early Spring 2008. Kronos's machine brought the Shadowlords into the world, and ethereal "echoes" of them could be engaged, fought, and slain by players. They occasionally dropped a rare Artifact Cloak called the Cloak of Corruption.
Some of the Shadowlords' followers comprise a Faction on the Felucca facet.
The Shadowlords from Ultima Lore
The Shadowlords were introduced to the Ultima world in the game Ultima 5: Warriors of Destiny. They were much the same as they are in UO. In that game, they kidnapped Lord British and turned Lord Blackthorn evil, in a manner similar to how Exodus did something very similar in UO.
Under their reign, and Lord Blackthorn's, the Virtues were twisted into evil parodies of themselves. (For example, violating Honesty meant that the "offender's" tongue was cut out, and someone who fled in battle, thus violating Valor, was executed, regardless of the circumstances of the flight.)
Ultima 5 is, for obvious reasons, considered one of the darkest of the Ultima series.