Sigma is an evil Reploid from the future of Earth 20XX and an adversary to X and his various allies. After forcing Dr. Ivo "Eggman" Robotnik to construct a new body for him, he began going by the name Sigma-1. Later, after plugging himself into a massive new body that was fused with the Lost Hex, he became known as Sigma-2. After shedding that form and gaining power beyond even that granted by a typical Super Transformation, he became Sigma-3.