Dominus
From Destinypedia, the Destiny wiki
Dominus is a powerful and high-ranking position within the Cabal Empire, surpassing even the rank of Primus. These Warlords command elite Legions meant for conquest, outclassing the scout Legions the Guardians had faced for years.
Ghaul who commands the Red Legion and instigated The Red War is the only individual the Guardians encountered who possess the rank.