Who is the Night Haunter?
Over at Lexicanum they published a nice write up on the Primarch of the Night Lords. Thanks to Larry at BoLS for re-publishing this.
The Coming of the Emperor
The Great Crusade
The Horus Heresy
After the invasion of Terra, the Night Lords did not splinter and flee like the rest of the Traitor Legions. Instead, they continued to attack the Imperium, however, their tactics seemed to change, betraying a self-destructive desperation. The Night Haunter himself was gradually losing his sanity and sense of purpose that had earned the respect of his Legion, and in his last days would frequently erupt into fits of violence, incoherency, and sadism. Many, such as Sevatar, became disheartened at what their Primarch had become. The Emperor himself, wishing to disband the Night Lords forever, dispatched half the Callidus Temple of assassins to terminate the renegade Primarch.