Death knights are usually created by demon lords or evil deities. These evil undead warriors are most commonly raised from the ranks of blackguards, fighters, rangers, and barbarians, but a paladin who falls from grace near the moment of death may also become a death knight. Paladins who become death knights are subject to the same modifications as are presented for the blackguard in Chapter 2 of the Dungeons and Dragons Dungeon Master's Guide.
In Dungeons & Dragons 3rd Edition (and Version 3.5), a death knight has an aura of fear that will rout groups of low-level enemies, can channel powerful negative energy with a touch, and the ability to project explosions of fire and unholy energy.
Death knights are rare but may be found in any environment. They often choose fortified lairs such as old castles and towers.
Typical Physical Characteristics
The original Dungeons and Dragons Fiend Folio indicates that death knights are "lich-like". A death knight's physical form is that of its decayed body. The face is a blackened skull with patches of rotting flesh with two pinpoints of orange light in the eye sockets. The voice of a death knight is chilling, seeming to echo from deep within. Death knights were powerful people in life, and so they often wear expensive or magic clothing and armor. They are fond of wearing flowing capes to mark them as figures of importance
Death knights are (nearly) always evil.
Though death knights rarely work with their own kind, they often have a variety of undead servants such as skeleton warriors, liches, and banshees. Death knights often ride nightmares into battle. Given the nature of their creation they are also often in the service of some demon lord or god of evil.