For my money, Weyoun was the single most hilariously smarmy character ever in science fiction. All praise to Jeffrey Combs for creating such a massively entertaining character.
Weyoun excelled at taking in information, processing it, and then responding in a manner which, taken at face value, was submissive and appeasing, but subtextually calculated and disguising his true feelings.
Whether it was his manner of dripping with subservience, "The Founders are wise in all things," or his wisdom in understanding his place in the greater scheme of the dominion, he ruled all.
Odo: Has it ever occurred to you that the reason you believe the Founders are gods is because that's what they want you to believe? That they built it into your genetic code?
Weyoun 6: Of course they did. That's what gods do. After all, why be a god if there's no one to worship you?
Toward the later seasons his interactions whit Dukat and then Damar were always awesome.
Gul Dukat: War is such thirsty work. Don't you agree?
Weyoun: Perhaps if you didn't talk so much, your throat wouldn't get so dry.
DS9 had so many amazing secondary characters, but Weyoun is my favorite.
Weyoun: Pah-wraiths and Prophets. All this talk of gods strikes me as nothing more than superstitious nonsense.
Damar: You believe that the Founders are gods, don't you?
Weyoun: That's different.
Damar: [laughs] In what way?
Weyoun: The Founders *are* gods.