Nathrezim

Nathrezim (called dread lords or dreadlords in the Common tongue) are intelligent and cunning demons who were discovered and recruited to the ranks of the Burning Legion by Sargeras, the dark titan. "The mysterious beings of the Burning Legion called the dreadlords are also known racially as the Nathrezim. Little is known of their homeworld and even that is rumor.[6] They act as tacticians and lieutenants upon the field of battle in time of war, as well as being emissaries and agents for the fiery lords of the Legion, notably Kil'jaeden. During the Third War, they served as the Lich King's jailors, on the behest of Kil'jaeden, and commanded the Plague that swept through Lordaeron.
They are known to be extremely manipulative and masters of trickery; they are thal'kituun, the unseen guests.