Ivan was, in fact, pretty terrible. His private police outdid each other in trumping up conspiracies leading first to the torture and death of individuals, then families, then entire towns. At least twice Ivan marched them into a city thought of being disloyal and lead them personally in a murderous revenge on the population, torturing the hapless innocents with his own hands and then heaping them on a pile in the central square when done. He carried around a pointed staff to randomly stab people with. He murdered his own son (then again, so did Peter, though more legislatively). Some of his wives died naturally, some less so.

But this wasn't all That unique. Ivan grew up in the constantly scheming world of the boyars, where the two primary families murdered the hell out of each other on a regular basis in their constant jockeying for power. His only constant as a child was their violence towards each other and contempt for him. So, little surprise that he grew up to be a blood hungry demon...