NAME: Xavius MacLeod
SPECIES: Human/Reploid/Sentient Virus Fusion
AGE: 72
GENDER: Male
SIGN: Argo (Mobian Leo)
NICKNAMES: Sigma, Siggy, Big Sig.
POWERS: Powerful reploid-enhanced ki energy, super-intelligence, ability to create the Sentient Virus, inhuman strength, GammaDrive (used against Future Sakura).
BACKGROUND: Xavius MacLeod first entered the history of Mobius during the Great War, where he joined the ranks of the Outlander army to take revenge for his deceased wife, accidentally killed by the heroes of that time. Later collaborating with Ivo Robotnik, a fellow villain, he made numerous plans to exact further revenge on the Mobian heroes. He adopted the alias Sigma, and performed several mechanical operations on himself to increase his strength. As time passed, he became less and less human, replacing 87% of his body's tissue with robotic enhancements. His human compassion vanished with these replacements, and he became ruthless and obsessed with destroying Mobius. He stole Robotnik's research on genetic experimentation, and would go on to create 4 known creations: Akane, Rayne, Akuma, and Vile; injecting them with a specially created S-Gene to keep them under his control. After forcing Robotnik to restart an ancient battleship named the Death Eye, Sigma began his first attack on Mobius. Thanks to the heroic efforts of Sonic, X, and Akuma (who rejected the S-Gene and turned on Sigma), the attack was thwarted. Sigma, Akuma, and the Death Eye were destroyed.
In the aftermath, the creation Vile used his resurrective ability to bring the few surviving cells of Sigma back to life. Fitting his remains with robotic life supporters, Sigma was able to endure, leading a new group of loyal followers named the Sigma Brotherhood. Over the course of 1 year, they constructed an army of robotic warriors, and waited for their next chance to strike against the heroes. In the original timeline, his Brotherhood overthrew Metropolis and used the Dragon Emerald to revive his body, making him more powerful than ever. After defeating those who opposed him, Sigma appointed himself ruler of Mobius, renaming it Sigmus and constructing his capital city Sigmatropolis over parts of the ruins of Metropolis. In the altered timeline, a future version of Sakura Ayomi traveled back in time and caught the Brotherhood off-guard, killing all five of them and destroying the Nexus Emerald and the Death Eye's ruins. In his last act, Sigma activated his GammaDrive, gathering hundreds of pieces of the ruined ship into his body and forming himself into the massive GammaSigma. Still unable to overpower Future Sakura, his new body was obliterated into a billion unsalvageable pieces.