First Appearance: Soul Edge
The duality of man is a frequent topic in literature and art, so why can't it be in video games, too? Siegfried/Nightmare is the epitome of that concept. Siegfried wants nothing more than to destroy Soul Edge, while Nightmare only wants to indulge in its limitless power. This makes for one of the most fascinating characters in the entire series, and he was there from the very beginning. Now isn't that something? (Though, yes, we know they became separate entities by game III). With his huge range and strong attacks, he can be a menace all around the playing field. For us, there is no better character than Siegfried/Nightmare. Hell, many would consider him to be the main character of the entire series. You don't get much better than that.