Kamen Rider Den-O (仮面ライダー電王, Kamen Raidā Den'ō, lit. 'Masked Rider Electro-King'), stylized in English as 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. It aired on the Super Hero Time slot alongside Juken Sentai Gekiranger. The series revolves around time travel, trains, and personalities. It follows Ryotaro Nogami, an unlucky young man who becomes Kamen Rider Den-O with the help of time-traveling Imagin (spirits from the future). The show combines elements of comedy, action, and drama with a focus on time manipulation and the relationship between Ryotaro and the Imagin.

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 ten 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 three more released in the summer of 2010.