Mycroft. He's basically like Sherlock, but imagine someone older, colder, even more observant, and basically running the British government. Mycroft has manners, but he's like a supervill- Y'know, I think you'd get along with him, actually. He's a businessman. Sherlock can't stand him.

[And with good reason, as far as John is concerned given what happened with Moriarty's lie.]

I don't like him much, myself. Hadn't been living with Sherlock a day and the arsehole kidnapped me and tried to pay me to spy on Sherlock for him. All without actually telling me who he was.