Lord of the Seven Hells
From A Wiki of Ice and Fire
The Lord of the Seven Hells is a being who rules the seven hells associated with the Faith of the Seven.
Sam Stoops' wife believed that Rohanne Webber, Lady of Coldmoat, sold her unborn children to the Lord of the Seven Hells in return for being taught dark magic. He allegedly sent a demon to collect the child each time Rohanne gave birth.