Siegfried Schtauffen is one of the most central characters of the Soul series and the main protagonist in most of its installments. He is a mainstay of the Soul Calibur series and one of the most iconic characters in the franchise.
Siegfried Schtauffen was the son of the knight Frederick Schtauffen, but joined a bandit group known as Schwarzwind, becoming particularly close friends with Salia Olschmidt. During a raid on some knights who had deserted from the army, Siegfried decapitated their leader only to discover that he had killed his own father. Horrified, Siegfried convinced himself that someone else had done it and became obsessed with revenge, searching for the legendary weapon Soul Edge. Eventually finding it in Valencia Port, he claimed the cursed blade for himself and was Malfested, triggering the event known as the Evil Seed. Upon claiming Soul Edge, an entity from Astral Chaos entered Siegfried's mind and assumed the form of a silver-haired boy, manipulating him into embracing Soul Edge's will and becoming the monstrous warrior known as Nightmare.
After losing to Kilik and his comrades in the form of Nightmare, Siegfried awakened in an unfamiliar place. Though his consciousness was free from Soul Edge's grasp, he was unable to free himself from the unforgiving memories of his time spent as the cursed sword's puppet. Before long he was confronted with a memory he'd kept repressed deep inside: the memory of having killed his own father... "What have I done...?" he groaned. The remains of Soul Edge lay at his feet... For Siegfried, his true nightmare had only just begun.
Despite being overcome with remorse and despair, Siegfried refused to let himself die at the hands of those seeking vengeance for his crimes as Nightmare, and dedicated himself to preventing Soul Edge from falling into a new wielder's hands. However, the more he fought and the more foes he slew, the more Soul Edge began to regain its power. Encountering Sophitia, Siegfried dueled her - thinking she had come to claim Soul Edge from him. After the misunderstanding was resolved, Sophitia attempted to cleanse Siegfried's Malfestation with her divine powers, her advice strengthening his resolve to seal away Soul Edge once and for all. Even so, his mind was slowly being taken over by the cursed sword. Though able to barely cope while awake, his sleep was dominated by terrible nightmares and he would awaken covered in blood and surrounded by butchered corpses: Soul Edge would seize control of his body while he slept - turning him back into Nightmare - and use him to do its evil bidding. However, a ray of hope appeared in the form of the voice of Soul Calibur, which had been trapped in Astral Chaos and was being consumed by Inferno. Grasping Soul Edge's hilt, Siegfried allowed himself to be pulled into Astral Chaos - fighting to prevent the Spirit Sword from being corrupted and absorbed. While he was successful, Soul Edge was able to increase its hold over him - trapping him in Astral Chaos for some time - and began focusing its will on corrupting both Siegfried and Soul Calibur. Siegfried's soul would however escaped from the Astral Chaos, only to disappear into the Astral Chaos over and over again when he fell asleep. This would allow Inferno to possess his body completely as well as take on the guise of Nightmare and slaughter people.
While trapped in Astral Chaos, Siegfried despaired at Soul Calibur slowly being corroded by Soul Edge's malice and was approached by Acht, a mysterious entity resembling an androgynous silver-haired child. Acht claimed to have once been a traveling companion of Siegfried's, and that at some point after claiming Soul Edge but before becoming Nightmare, Siegfried had earned the favor of the Holy Roman Emperor and become one of the most famous knights in the world by slaughtering untold thousands of Ottoman Empire soldiers. However, Siegfried possessed no recollection of these events and rebuked Acht's attempts to manipulate him into giving in to Soul Edge's corruption and surrendering Soul Calibur to her; resolving to break free and regain control of his body the moment the opportunity presented itself.
During his time at Ostrheinsburg Castle, Siegfried gained knowledge of where Soul Edge's servants held imprisoned hostages; and was able to use the brief interludes where he regained control of his body to relay that information to Hwang before sensing he was turning into Nightmare again and departing, unwilling to cause more casualties.
In the Legacy of Chris Thorndyke,
And he is reprised by Roger Craig Smith in the English dub and Nobuyuki Hiyama in the Japanese dub.