Mario is perhaps the only video game character that every gamer and most non gamers have heard of.
Sephiroth- no WAY. I've like never met anybody who knows who Sephiroth is.
Sonic- I'm guessing most gamers know him, but not as many as Mario.
I honestly cannot think of another character even nearly as famous as Mario. Master Chief and Link are famous within the gaming community, but not outside it.
Does Pikachu count?