Persuasion
This does not necessarily have to do with how one speaks or acts, but encompasses everything about how someone pulls others' strings. This comes in handy when trying to haggle for a better price on that nifty longsword/can opener, planting rumors, or trying to convince the king he'd be better off naming you as heir.
Characters with poor Persuasion scores can't lie to save their lives, rarely get what they want, and fall short at good come-backs. Characters with a good Persuasion score are manipulative and convincing: they make great liars, negotiators, insult comics, and flirts.
Persuasive people are those such as statesmen, upper management, and con artists. Persuasion has many uses, some very nefarious. Adolf Hitler and Joseph Stalin were both Persuasive and convinced many to do terrible things.