The final villain claims to be a “consulting criminal”.He is smart and cunning, acts low-key and cautious, and has countless subordinates.Consider Sherlock Holmes a powerful enemy, and all cases are more or less related to him.He created a series of cases and even threatened people around Sherlock and Watson, just to completely defeat Sherlock.
In S2E3, he had a duel with Sherlock on the rooftop and shot himself to death in order to force him to commit suicide.