Oma Zi-O

"You fools could never defeat me. And do you know why? Because I was born to be king!"

- Oma Zi-O boasting about himself.

Sougo Tokiwa (in Japanese: 常磐ソウゴ, Tokiwa Sōgo) is the future self of the titular Kamen Rider Zi-O, Sougo Tokiwa, who achieved a nigh-omnipotent status in the future and rules the Earth in the year 2068 as Oma Zi-O (in Japanese: オーマジオウ, Ōma Jiō), also commonly referred to as the Demon King (in Japanese: 魔王, Ma Ō) by Tsukuyomi.

He is the overarching antagonist of Kamen Rider Zi-O, being the reason that most of characters travel back in time, either in order to stop him by eliminating Zi-O, or coronating a person other than Sougo to be Oma Zi-O.

He was voiced by Rikiya Koyama, who also played Kagetane Hiruko, Giovanni in Pokémon Origins, Kiritsugu Emiya, Kamen Rider Bujin Gaim in Kamen Rider × Kamen Rider Gaim & Wizard: The Fateful Sengoku Movie Battle and Paradox Roidmude in Kamen Rider Drive: Surprise Future.

History
On a day known as the "Day of Oma", Oma Zi-O conquered the world with seven machines called "Dai Mazines", using his vast powers and time manipulation to wipe out half of humanity and subjugate the rest. A resistance soon arose to oppose him, but Oma Zi-O easily suppressed them. In the first episode, he is seen using his powers to fight them off before boasting of the fact that he was "born to be king". Unable to defeat Oma Zi-O in the future, two members of the Resistance, Tsukuyomi and Geiz, traveled to the past to change the future by changing his past self's fate of becoming Oma Zi-O.

After Sougo Tokiwa was flung into the future by Kamen Rider Decade, Oma Zi-O had Dragreder bring his past self and Tsukuyomi to him. The Demon King reveals himself as Sougo's future self, shocking the past Sougo. Deducing that his past self was in denial about becoming the Demon King, the future Sougo tells his past self that it's their destiny to become king and "save" the world. Angered, the past Sougo transforms into Kamen Rider Zi-O and attempts to attack his future self, but the future Sougo transforms into his Kamen Rider form as well and beats him down. As Oma Zi-O continues to pummel Zi-O he offers his past self a choice, telling him that if he doesn't want to become the Demon King then all he needs to do is destroy his Ziku-Driver. Soon after Oma Zi-O launched an attack that forced Sougo out of his transformation. Oma Zi-O then opens a window in time to display his servant Kasshin beating down Kamen Rider Geiz Faiz Armor. Oma Zi-O tells his past self to return to 2018 and creates a time portal to allow the past Sougo and Tsukuyomi to travel through back to their time.

Future Sougo then reverts his transformation and takes a seat on his throne. In 2018, Sougo allowed Geiz to destroy his Ziku-Driver causing Oma Zi-O to be erased from the timeline. However, Sougo would later become Kamen Rider Zi-O again, and as a result his future was restored as well. As he's returned to existence, the future Sougo let out a laugh, revealing he knew what decision his past self would make.

Trivia

 * His name can alternatively be spelled as "Ohma Zi-O" with the first word being an anagram for "Maoh" which in Japanese means "Demon King".
 * Befitting the series' motif as a summarization for the entire Heisei Kamen Rider continuity for the past 19 years, Oma Zi-O shows resemblence and similarities to other previous Heisei Kamen Rider villains, on characteristics and physical appearance, including:
 * Oma Zi-O shares similar name to Prime Minister Orma / Kamen Rider Sorcerer, and they both have the color gold as their color theme.
 * Oma Zi-O is a villainous rider connected to time and/or time-travel, just like Kamen Rider Bujin Gaim and Kamen Rider Dark Drive. All three are also evil counterparts from another era to the heroic Riders, although Bujin Gaim is from the past, while both Dark Drive and Oma Zi-O are from future. In addition, they all share the same voice actor.
 * His red eyes and golden Rider armor bears chromatic resemblence on Tenjuro Banno as Gold Drive and Masamune Dan as Gamedeus Cronus.
 * Like Bat Fangire (as the original Kamen Rider Dark Kiva) from Kamen Rider Kiva, Oma Zi-O is the evil counterpart to a heroic character with the same Rider Armor (P.S. Taiga Nobori became Dark Kiva in the finale of Kiva). However, Oma Zi-O is the future evil counterpart of Sougo himself, while King is both the father and past predecessor to Taiga. They also both have "King" in their title.
 * Curiously, Oma Zi-O's "eyes" resemble to shape of an eagle, possibly hinting at a connection to Shocker. The logo of Zi-O, which is depicted on Oma Zi-O's forehead, also shows an "X"-like symbol, which could perhaps hint at a connection to Foundation X as well.