Live action TV
Description
In the narrative of Kamen Rider Decade, the character known as Apollo Geist primarily operates under the human alias of Guy. This villain is a high-ranking executive of Dai-Shocker, a coalition of evil organizations from across different realities. Guy serves as the organization's Security Chief, a position that charges him with hastening the convergence of the nine parallel worlds to make them easier for Dai-Shocker to conquer and dominate.

When confronting his enemies or carrying out his duties, Guy invokes the command "Apollo Change" to transform into his true, more powerful form as Apollo Geist. This version of the character is a reimagining of a villain from the much earlier Kamen Rider X series. In this iteration, Apollo Geist is a revived entity with a critical flaw: his lifespan is extremely short. To combat this and sustain his own existence, he relies on a device called the Perfecter, which is mounted on his face, to forcibly absorb the life force or "life flames" from human beings.

Personality-wise, the Decade incarnation of Apollo Geist is depicted with a distinct lack of honor, contrasting sharply with his original counterpart. Guy is an arrogant, snide, and fundamentally cowardly villain. He frequently proclaims himself to be the "greatest nuisance in the universe" and has no qualms about using the most underhanded methods to secure victory. His tactics often involve taking hostages, including children, and he has a persistent habit of underestimating his opponents, a flaw that repeatedly contributes to his defeats. Despite his high rank and immense power, his actions are driven not by ideology but by a desperate, self-serving need to survive and a ruthless ambition to see Dai-Shocker's plans succeed.

Within the story, Apollo Geist serves as a primary antagonist, a persistent adversary for the protagonist Tsukasa Kadoya, the titular Decade, and his allies. His role is to act as the field commander for Dai-Shocker, personally leading the invasion of various A.R. Worlds. He is first seen in the World of Black RX, where he easily overpowers Decade and seriously injures Natsumi Hikari, a key companion of the heroes. Throughout the middle portion of the series, he is a recurring menace, chasing Decade through worlds such as the World of Black and the World of Amazon. In the World of Amazon, he is shown brainwashing children as the principal of a "Dai-Shocker School" and manipulating a young boy into betraying Kamen Rider Amazon, proving his willingness to corrupt and endanger the innocent for his goals.

His key relationships are largely antagonistic. He is a direct foe to Tsukasa Kadoya and Yusuke Onodera, the world's version of Kamen Rider Kuuga. He also has a transactional rivalry with Daiki Kaito, Kamen Rider Diend, who successfully steals his precious Perfecter device, leading to a major turning point for the character. When his Perfecter is later destroyed by Decade, Apollo Geist loses his primary means of sustaining his life. In a desperate scheme for a new source of power, he arranges to marry Yuki, the Queen of the Fangires from the World of Kiva. Through this union, he gains the abilities of a Fangire and transforms into a more powerful entity known as Super Apollo Geist.

This evolution marks his final development. As Super Apollo Geist, he gains the terrifying ability to accelerate the fusion of the different worlds, which causes entire realities and the Riders within them to begin disappearing. He also gains the power to revive the various monsters and villains that Decade had previously defeated, resurrecting them to serve as his army in a final confrontation. In his ultimate scheme, after Yuki is destroyed, he kidnaps Natsumi Hikari, intending to force her to become his bride and a new source of life energy. In the climactic battle of the Rider War world, he demonstrates his power by defeating Yusuke Onodera. He is ultimately destroyed by a combined attack from Decade's Complete Form and Diend's Dimension Shot, but his final words are a defiant promise that he will one day be resurrected again as the universe's greatest nuisance.

Notable abilities define his threat level. In his standard Apollo Geist form, he is a formidable combatant, strong enough to defeat Decade in their first encounter. He wields an array of weaponry, including his favored gun called the Apollo Shot, a thin sword named the Apollo Foil, and a sturdy, bladed shield known as the Geist Cutter which can be thrown like a boomerang. His fighting style is pragmatic and brutal, combining ranged bombardment with powerful melee strikes, and he often summons other monsters to fight alongside him. As Super Apollo Geist, his abilities are magnified; his signature power is the capacity to accelerate the convergence of parallel worlds, effectively erasing other realities from existence. He also wields an enhanced version of his pistol to fire powerful energy blasts. These abilities, combined with his cunning and lack of scruples, make Apollo Geist one of the most dangerous and persistent villains that Kamen Rider Decade must face.