OverLord

The OverLord (オーヴァーロード) is the highest power among the Unknown, and is referred to as the creator of the human race. Long ago, there existed twin entities; one being the embodiment of light while the other was embodiment of darkness. These twin 'brothers' co-existed in harmony for a time, eventually creating our world. However, neither could agree on who would reign over their creation and a battle for control took place. In the end, the Overlord of Darkness triumphed over his brother, the Overlord of Light. But with his dying breath, the Overlord of Light bestowed his essence upon humanity—the power of Agito—with the hopes that, one day, they would evolve beyond his control. But the Overlord of Darkness refused to let this occur, taking it upon himself to personally eliminate the vessels of Agito, creating the Lords to kill all humans who possess the potential to "evolve" into Agito.

Though he died around the Pleistocene, the Overlord of Darkness left a puzzle that held a model of his very own DNA. Once the puzzle was solved, the Overlord's DNA was reconstructed from scratch. This allowed him to reform his physical body, starting off as an infant as he broke out of the containment box and escaped from the O-Parts lab. However, his birth was witnessed by Sakiko Mikumo, following her after he matured to an eight-year-old boy until she was killed by Anguis Femineus, whom the Overlord punished. Encountering Ryō as he was near death, the Overlord used his power to prolong his life, assuming his adult form as a result. After forced to take his leave after being nearly killed by a fear-driven Gills, the Overlord took it upon himself to personally murder Tomoko Miura, getting arrested and placed in a mental ward after he shut down from the burden of personally killing a human. As a result, the Overlord decided to watch from the sidelines as the Lords committed various supernatural murders on anyone reaching paranormal maturity, though he intervened once to give Agito's Tornador a power-boost. It would later result with Shōichi, along with Ryō and Makoto Hikawa, further complicating matters and interfering in his emissaries' work.

Before long, casualties mounted on both sides, with paranormals and Lords alike suffering loses. But the lost of the El of the Sea opened the eyes of the Overlord to the reality that the vessels of Agito, Shōichi Tsugami, Ryō Ashihara, and Kaoru Kino had grown too powerful. To this end, he would see to it personally that all active Agito vessels were hunted down and stripped of their Seeds of Agito, rendered powerless. However, the Overlord realized he needs to kill the Riders in order to quell the Seeds he already absorbed. But with Hikawa's aid, Shōichi dealt a decisive blow to the Overlord that released the Seeds of Agito back to their rightful owners and forced the Overlord to retreat. However, that shock that even normal humans had grown strong enough to oppose his power convinced the Overlord that humanity was no longer worthy of existence, and so began orchestrating their extermination and start anew.

The Overlord would put his genocide of humanity into action: realigning the constellations of the Zodiac, ultimately killing off all of mankind in bizarre doppelgänger homicides starting with those born under Scorpio. To do this requires tremendous concentration, which would render him vulnerable. To this end, he creates the El of the Wind to be his bodyguard and the El of the Ground to continue killing those reaching paranormal maturity. But the Riders make one final stand and with the El Lords destroyed, the Overlord attempts to retreat but is wounded by Agito's Shining Rider Kick. The Overlord survived the attack and has a conversation with Tetsuya Sawaki before the latter died, the latter's words convincing him that while he created mankind, the Overlord didn't truly understand them. After which, he hints that he decides to postpone his plans and observe how humans will use their own gifts and whether or not they are worth of existing.