Z-one is the final antagonist of Yu-Gi-Oh! 5Ds, and the true antagonist of the entire series, being responsible for many of the series' events, including the founding of Yliaster and the splitting of Satellite and New Domino City. He is a scientist who hails from a post-apocalyptic future, having traveled back in time to alter history and prevent said future from happening by any means necessary.
Z-one was a scientist from a time in which humanity used Ener-D to control and accelerate their own evolution, but did so with greedy and selfish desires. Eventually, their Ener-D went out of control, creating an army of Meklord Emperors to destroy the human race. Researching how to stop them, Z-one discovered a way to stop thier power source: the Ener-D and the Planetary Pieces in people's hearts. Realizing that he alone wouldn't be able to inspire others, Z-one researched into the life of Yusei Fudo, a legendary duelist who saved New Domino City long ago. He then proceeded to perform a surgery on himself in order to take on Yusei's appearance, as well as implant a device into his head to make him think like him. Unfortunately, while Z-one's actions did inspire people to help each other and caused the Meklord Emperors to stop attacking; he was too late as Ener-D proceeded to explode, destroying society and leaving only a few survivors. Z-one survived however, though the device in his brain was now broken, and he lost faith in humanity.Eventually, Z-one encountered three other survivors; Antimony, Aporia and Paradox. Together, the four men spent many years researching ways to prevent the downfall of mankind by traveling onto the past. Unfortunately, they grew old while doing so, and Antimony, Aporia and Paradox eventually died, while Z-one made himself a cyborg in order to prolong his life. He sent an embodiment of Paradox back in time to kill Maximillion Pegasus, in order to wipe the Duel Monsters card game from existence and thus prevent Ener-D from being created. Menawhile, he sent embodiments of Antimony and Aporia back to the time of Yusei Fudo; while Antimony was meant to help Yusei in his growth, Aporia (who was split into three embodiments of his despair, which took the form of his youth, adulthood and old age) was sent back in time to complete the Grand Design, which would open a time rift large enough to bring the Divine Temple, Z-one's headquarters built from the ruins of New Domino and Satellite, crashing into New Domino City and destroying it. In doing so, Z-one would take countless lives, but would also destroy all traces if Ener-D in Yusei's time, thus preventing his future from ever occurring.