Warden of Eternity.
The Warden Eternal, Created by a race known as the Celestials. They created the Warden Eternal to enforce the supernatural beings such as Devils, Angels, and Fallen angels alike.
Along with the Grand warden, human counter part of the Warden eternal, serves the Celestial's will.
When the war of the three factions were at its peak, The Celestial sent their two enforcers to stop the war between the three factions.
However, They failed their task, During the Warden's attempt, The three factions -- having no knowledge about the origins of the Warden and The Celestials -- The three factions viewed the them as a threat to their own sovereignty.
The three way war raged for centuries having Warden trying to save what's left of humanity.
With the use of the Sacred gears and the three factions conscription of more humans. Both of them gave one final attempt to stop the war.
Ultimately, their attempt failed.
Having Spectating their two enforcers fruitless attempts to try and stop the war, The Celestials finally decided to use force, authorizing the two Wardens to unleash their full might against the three factions.