*Nightmare is the main antagonist of the Soul series. He made his first appearance in Soul Edge, with his proper debut being in Soulcalibur. He is the host, wielder and living incarnation of the cursed sword, Soul Edge, the objective of most other characters in the story.

Nightmare has been portrayed in the games as a violent and ruthless creature, constantly in search of souls to restore Soul Edge.

He looks down on humans, considering them "pathetic" and "foolish", having no mercy for others, even to those who fail to serve him, as shown to the members of his Schwarzstrom team who he treated as pawns. The only one who he treats with some respect is Tira for being just as violent as him, however he has still thought about taking her soul on occasion. His incarnation in V wants to take over the world rather than destroy it.

True to his nickname, Nightmare appears as a dark figure covered in dark blue armor that covers most of his body.

His prominent feature is his right arm, which has been twisted and transformed into a large three-digit claw whose flesh overlaps his entire right arm and shoulder. He is depicted with Soul Edge in his left hand, symbolizing his polarity with Siegfried. Over the years, his appearance has progressively grown more and more demonic, as influenced by the state of Soul Edge himself.

During the events of Soulcalibur, he was simply a suit of armor with a giant arm and horned helmet. In Soulcalibur II, Nightmare's armor changes design, now sporting long red hair from the back with bat wing-like ornaments on the sides replacing the horn. With a body to call his own at last, Nightmare returned to a suit similar to his original Soulcalibur variant, although slightly re-vamped, in Soulcalibur III, with the claw having stretched over his chest plate, possessing a rudimentary jaw lined with sharp teeth both on his shoulder and chest.

Nightmare has been present in one form or another due to him being an animated armor, his possessing of bodies or the power of Soul Edge keeping him alive.*