Captain of the Guard is a position usually held by an officer of a Great House army. The holder of this position was in command of the personal guard of the head of the House.
In House Harkonnen during the time of the Faufreluches, the Captain of the Guard was a prestigious position, albeit one that also possessed great peril. The captain of Baron Vladimir Harkonnen's personal guard was killed by the poisoned tooth used by Duke Leto Atreides when he was captured by Harkonnen forces. As a result, Corporal Nefud, who had shown leadership qualities and bravery during the ensuing chaos, was promoted to the position. However, Nefud managed to incur the Baron's wrath on many future occasions for apparent failure.
Behind the Scenes Edit
Presumably, the position of Captain of the Guard was one maintained by many Great Houses of the Imperium.