Ex-high-ranking angel (Throne) who studied demons and dark arts out of forbidden curiosity. He researched the origins of their true nature, are they evil or do they become evil ? How do they corrupt ?

Attempted fusion of angelic and demonic forces: During his studies, he attempted a forbidden fusion.
Trying to weave a demonic principle into his holy armor; a test to see if he could create a "perfect" hybrid. A balance of heavenly discipline and demonic adaptability.
It failed...violently.
The backlash ripped through his body.
His summoned armor turned on him for a split moment, sensing heresy, but it was corrupted by demonic energy before it could do anyting.
In the explosion of celestial and infernal energy, he lost his left eye, forever marked by his "betrayal."

Soul: Mostly angelic, tainted just slightly, enough that both Heaven and Hell distrust him.
Powers: Can summon corrupted armor linked to his tattoo.
He is more empathetic than other Angels. He was not born with the hatred of Hellkind. And that "humanity" and curiosity cost him his place in Heaven.
He could not be killed, as his death would cause unrest among other angels. His armor could not be removed either, as it is linked to his soul.