That he was Snoke's protege and apprentice, the one he was grooming to take his place. Before they developed Starkiller Base, they said he was the most lethal weapon in the First Order, and their best interrogator. That he was dangerous, volatile, angry. Someone whose bad side you didn't want to be on, even if you were on his team. That he force-choked one of his own soldiers for bringing him bad news, more than once. That he was ruthless. That he was stronger in the force than anyone else in the galaxy, that he could read your mind.
Some people called him the Jedi Killer -- they say he was one of Luke Skywalker's Jedi trainees, but one night, he just-- decided to burn down the base and kill all of the Jedi. As far as we know, he and Skywalker were the only survivors.
There was also this one guy who kept telling me that he had an 8 pack. I don't know what that was about.
I know some of it was bluster and propaganda, but I don't know how much.