Kamen Rider Den-O (仮面ライダー電王, Kamen Raidā Den'ō, Masked Rider Den-O) is the seventeenth installment in the popular Kamen Rider Series of tokusatsu programs. It is a joint collaboration between Ishimori Productions and Toei. It premiered January 28, 2007 on TV Asahi, and concluded airing on January 20, 2008. Its lead actor Takeru Satoh is the first Kamen Rider Series lead born in the Heisei period of Japanese history.

Along with the usual film adaptation that Heisei Kamen Rider series have released during the late summer of their broadcast run, Den-O had a second film released in the spring following its broadcast run which grossed 730 million yen (approximately US$6.8 million) and a series of 10 OVA shorts, both of which are firsts for any Kamen Rider. Continuing the trend, Kamen Rider Den-O also had a third film released in October 2008, the first for any Kamen Rider series and a second series of 12 OVA shorts was released in November 2008. Takeru Satoh claims that the reason that Den-O has amassed such popularity is because of its comedic timing. A fourth film was released on May 1, 2009, and a fifth is purported to be scheduled for release in June 2010.

The catchphrases for the series are "Traveling through time, I am here!" (時を超えて 俺、参上!, Toki o koete ore, sanjō!) and "The time train, DenLiner! Will the next station be in the past or the future?" (時の列車デンライナー!次の駅は過去か?未来か?, Toki no ressha Denrainā! Tsugi no eki wa kako ka? mirai ka?).

Synopsis

Ryotaro Nogami is a young man with a lot of bad luck. One day, he finds a strange pass and things got stranger from a mysterious girl and a large time-traveling train to being possessed by an entity called an Imagin, beings from an alternate future whose kind are attempting to change the past. Though slightly confused about the nature of the crisis, Ryotaro, along with the aid of the hot-headed, violent Imagin, dubbed Momotaros, becomes Kamen Rider Den-O, traveling to different times on the DenLiner to battle the evil Imagin to prevent them from altering the past to affect the present and future. During his adventure, Ryotaro is joined by other Imagin who aid him as well; the lying, manipulating and womanizing Urataros, the herculean (and narcoleptic) Kintaros, and the childish yet powerful Ryutaros. He later meets the mysterious Yuto Sakurai and his bumbling Imagin partner Deneb. Yuto is not only Kamen Rider Zeronos but is the younger incarnation of Ryotaro's older sister Airi's fiance, Sakurai, who mysteriously disappeared and is tied to the mysteries involving the Imagin and a person known as the Junction Point.