If you would honor the prospect of entertaining my humble idea of a character once one of the highest ranking human servants of GOD, corrupted, leading to the ultimate self-betrayal and as a result cursed by the very GOD he once worshipped. 
"Cursed to never age, cursed to never cease existing and cursed with a subconscious obsession, even engraved in his soul, to seek the most excruciatingly agonizing pain and experience it."

Basically an immortal piece of torture meat. I don't think I'll even give him any powers, well except indestructibility and the more his regeneration takes the faster it becomes so no throwing him in the lava and be done with him but he still feels the pain fully. And even if he is disintegrated in one hit he will regenerate, starting with the skeleton, brain/heart, the organs, muscles/blood, then skin/nails/hair. He doesn't need to sleep/drink/eat/breath etc, basically his one and only required purpose is to feel pain. Hopefully someone will reach to his soul and lift the curse...