As with Ultraman: A Special Effects Fantasy Series (1966), this series, created by manga artist Shotaro Ishinomori, gave birth to another popular type of modern Japanese superhero: The "Henshin" (Japanese for "transformation") Hero. These are normal-sized superheroes who transform into a cyborg, android or mutant by performing a "henshin pose," and usually fight their enemies with martial arts, minimal weaponry and a finishing attack (usually a flying kick). The Sentai Series (starting with Ishinomori's Secret Squadron Gorenger (1975)), Metal Heroes (starting with Space Sheriff Gavan (1982)) and hundreds of other contemporary Japanese superheroes were an offshoot of this historically-important genre.
Star 'Hiroshi Fujioka' fractured his thighbone in a motorcycle stunt for Episode 9 ("The Terrifying Cobra-Man") and was out of commission for a time. As a result, until Episode 13 ("Tokageron and the Great Monster Army"), his Takeshi Hongo/Masked Rider character was milked out for another four episodes by having him stay in costume (but played by another actor) or stock/unused footage of Hongo out of costume was used, and was dubbed over by voice actor Rokurô Naya. But this could not be carried out indefinitely, for after several options at the Toei Studio, they decided to introduce "Masked Rider 2"/Hayato Ichimonji (played by Takeshi Sasaki), to take over after the fallen star. After two guest appearances, Fujioka returned for good in Episode 53 ("Monster Jaguarman - Deathmatch by Motorcycle Fight"). The show then had two heroes (as opposed to one).
This show has similarities with another creation by Shotaro Ishinomori: "Cyborg 009," where the nine heroes are turned into cyborgs by the villains, but escape to fight them. This time, it's one hero (and later, two).