Diavolo is a tall, fit, pale, man with a somewhat athletic build. He's paranoid, valuing his privacy and anonymity above all, killing those who find out who he is. Outside of his paranoia, he is an unpredictable, cold, and calculating man. You've discovered his identity and fled, he clearly had to track you down and eliminate you himself. Not everyone has the skill it takes to unearth who Diavolo was, after all.