Death Knights

A Death Knight is an undead evil warrior.
In life, Death Knights were Knights or Paladins who, through some dark 
deed betrayed themselves and their beliefs. The Knights’ soul became 
darkened and was not allowed peace in its final rest.
Death Knights are a frightening sight. They are generally wearing plate 
armor and weilding nasty-looking weapons. Underneath their armor, Death 
Knights resemble Zombies; rotting flesh, tattered clothing, sickening 
smell, etc.
Death Knights possess human-level intelligence. It is believed that they
 have spell casting abilities, and some spell immunities. It has been 
reported that some retain their riding abilities and are mounted on an 
undead steed called a Nightmare.