People have speculated that it might be a higher member of The Rogues, maybe his girlfriend, or even The Riffs. Well finally, we can put this one to bed as David Patrick Kelly responds:
"Walter and I didn't talk too much about who Luther was speaking to on the phone . I think he only said "the Boss". I made up a character as "the Boss" who combined political corruption with gangsterism, someone Luther knew from a young age, a kind of mentor who Luther was anxious to please, a kind of Fagin/Boss Tweed. "
So there you have it!
