From Destinypedia, the Destiny wiki
The Blood Guard is an elite unit of the Red Legion. Described as Dominus Ghaul's "chosen" and would die for their leader, they often serve as commanders of operations throughout the Red War and can also be found serving as bodyguards to high-ranking Cabal officers. They can be identified by their heavy, all-red armor, which often features prominent horsehair-like crests.
The Blood Guard has members filling the roles of Legionnaires, Incendiors, Centurions, and Colossi and are frequently seen serving as an Honor Guard centered around Red Legion Hardpoints or points of interest. It is heavily inferred Blood Guard are also enforcers amongst the Red Legion to help carry out the will of the Dominus or acting Red Legion leader along with serving as a royal guard and field operatives. Considering the Legion's armor scheme with commanders and Ultras wearing Gold, his personal bodyguard along with the Guard's instability after his fall, it can be inferred Thumos, the Unbroken was a commander of the Blood Guard if not its leader.
In Ca'our's short eight-month reign, the Blood Guard were encountered far more frequently in the field until his subsequent death where the Blood Guard began to fracture into individual lead cells as their primary purpose for existing had been shattered. The largest case was several Blood Guard defecting to the "Unbowed Legion" of the Cabal Deserters in the form of Uprooted Red Legion.
Following the events of the Empress' arrival into the Solar System, the remaining Blood Guard have resurfaced amongst the fields of multiple Battlegrounds acting as field commanders, shieldbearers, and unstable fuel cell holders.
Known Blood Guards
Blood Guard Units
List of appearances