Daisuke Yamamoto (山本 大介?) was an infant around the time of the plane he and his family were on crashed in the Amazon rainforest, leaving young Daisuke the sole survivor and grew up as a wild child, living off the land under the name of "Amazon" (アマゾン?). However, Daisuke's idyllic existence is cut short when the Ten-Faced Demon Gorgos, massacres the village in search of the powerful "GiGi Armlet", which gives the bearer fantastic power. Elder Bago, last of the Incas, gives the GiGi Armlet to Daisuke for safekeeping while using his knowledge of Incan science and magic to perform a mystical "operation" on Daisuke, transforming him into the powerful Kamen Rider Amazon before he died.
Under Bago's instructions, Daisuke evades Gorgos and searches for Professor Kōsaka, who knew the nature of the Gigi Armlet. Meeting Kōsaka's nephew Masahiko Okamura, who obliges to teach him to speak and the ways of the world, Daisuke is infuriated at Kōsaka being murdered by the Kumo Beastman and drives him off to save Masahiko and his sister Ritsuko Okamura, who blamed him at first for her uncle's death until he made an antidote to the poison her friend Masako got from the Beastman Vampire Koumori. Though in the first half of the series, because he was isolated from any human contact as a child, Daisuke could not speak coherent Japanese and say only a few words. But through Masahiko helping him cope with the culture shock, Daisuke learned to speak properly.
While catching fish, Daisuke finds himself at a motocross, frighted by the culture shock before he saves a man named Tōbei Tachibana who was attacked by Kamakiri Beastman. Paying him back, Tōbei helps Daisuke overcome his fear of motorcycles to save Masahiko from the Akajuusha before Kamakiri attacks them, with Amazon killing the Beastman. But unnerved about why he is hunted by the Geddon, Masahiko learns of Yamamura, one of the members of Kōsaka's exploration party into the Amazon. Hoping to find the answer, they and Tōbei learn that Yamamura's on the run from Geddon as he holds the secret that Geddon would go to lengths to make silent. When Beastman Omukade captures Yamamura and his daughter, Daisuke pursues with newly built Jungler, saving them before killing Omukade. During the fight, Yamamura is fatally wounded by the Akajusha as Yanamura reveals the "GaGa Armlet", the counterpart of the GiGi, that Gorgos possesses before he died.
During the Mogura Beastman incident, Daisuke is arrested by the police for attacking an officer when they needed to know his identity in spite of his part in helping them get murderer Oshima. Though bailed by Tōbei, a confused Daisuke runs off with a hatred for humans. The next day, Tōbei and Ritsuko find Daisuke as he intends to return to the Amazon. Learning that Masahiko was abducted by Mogura and at Ritsuko's pleas, Daisuke saves his friend and give Mogura a severe beating. Daisuke later finds Mogura being punished for failing Gorgos, saving the Beastman who is shocked. Later, after being told by that Johoku University has gained relics from the Amazon that might shed some light, Daisuke and friends investigate and find the mysterious Quipu which Daisuke could decipher. But the Beastman Yamaarashi arrives and steals the Keep with Daisuke falling into his trap. But with Mogura's aid, Daisuke learns the story behind the GiGi and GaGa Armlets before killing Yamarashi, now knowing Geddon's goals.
While searching for Geddon, Daisuke receives a radio from Masahiko so he can know when Geddon's up to no good. After saving a woman from Kani Beastman, Daisuke learns that Mogura is forced by the monster of reveal Ritsuko as a potential weakness. Though he attempts to protect Ritsuko, Daisuke is saddened as she tells him that he's the one Geddon's after and it might be best for everyone if he just goes back where he came from. In spite of this, Amazon saves Ritsuko and friend from Kani and later receives a vest from Ritsuko as her way of thanking him. Eventually, Amazon faces off against Gorgos himself, destroying once he rips the GaGa Armlet off of him. However, the GaGa Armlet then falls into the hands of the Garanda Empire, led by the ruthless Great Emperor Zero. Amazon continues his fight against evil, eventually toppling the Garanda Empire and retrieving both bracelets. With his mission complete, he returns to the amazon forest where he lived because it is his true home, though Tōbei believes that he will come back if evil comes to terrorize Japan again.
GiGi Armlet (ギギの腕輪 Gigi no Udewa?) is a mysterious O-Part of the Incas that was created 120 years ago as one of two keys that would allow the user of the two to rule the world with Incan super science. The GiGi Armlet serves as Amazon's power source along with being the only thing keeping him alive. Grafted unto his left arm, Daisuke is originally unaware of the Armlet's true power until he found the Quipu that revealed it.
Condorer (コンドラー Kondorā?) is Amazon's belt. While not the means of Amazon's transformation like Riders before and after, it has other uses such as a grappling hook.
The Jungler (ジャングラー Jangurā?) is Amazon's motorcycle, built by Tōbei Tachibana based on design specs provided by Kōsaka from his journey into the Amazon. The Jungler is much more vibrant and exotic than Tōbei's previous creations, featuring "wings" on the back and a "mouth" and "eyes" on the front. In Kamen Rider Spirits, the Jungler has a hidden grapple cable and winch in the "mouth" of the bike used to scale high terrain.