In my 4E Dromenon campaign, one of the big villains was the Ashen God, Eater of Souls, God of Undead, Decay, and Betrayal. He was served by a cult known as the Glassmakers, a splinter group of the capital’s glassblowers guild, who harvested souls for their deity to eat.
The Ashen God was originally the Apostle Iscariot, who betrayed the Messiah. He fled into the Elemental Chaos, followed by Zebulon, one of the other Apostles. When Zebulon caught up with him, a fight ensued, and Iscariot was incapacitated, pinned to a black monolith by Zebulon’s sword. Of course, you shouldn’t disturb Evil Black Monoliths in the Chaos: Iscariot merged with the entity trapped in the monolith and became the Ashen God.
My favorite bit involving the Ashen God was when the party tried to enter one of his monoliths in order to kill the high priestess inside. The smooth black surface didn’t reflect their own faces, but that of the Ashen God, who asked: ‘Who will you betray in my name?’
Of course, this being 4E, the party fought him in the end: think Vecna wielding Stormbringer. (Literally: I based the stats on info found in the Monster Builder.)