The Gamma, alternatively spelled as Ganma, are a group of extra-dimensional beings who reside in the World of Gamma and are the main antagonists of Kamen Rider Ghost.
The Gamma were originally a village of humans led by Adonis who worshipped a giant monolith. After their continued prayers for a world without poverty, the Great Eye brought them to the World of Gamma.
After losing his wife and eldest son to disease, Adonis began to wish for a world where tragedies would never occur. To fulfill his friends' wish, Edith invented a form of immortality for the Gamma using the separated consciousness of Eyecons and body-preservation via life support capsules.
In order to prevent unnecessary contact with the Great Eye, Edith created a set of fifteen artificial beings called the Gammaizers to protect it. However, flaws soon began to appear in the life support system, with the Gammaizers blocking Edith from being unable to do anything about it.
Edith later traveled to the human world and began working with Ryu Tenkuji and Chikara Saionji to find a way to counteract the Gammaizers. However, Chikara betrayed them both and made a deal with Igor to transport the Fukami siblins to the Gamma World so he would have human samples to study.
The Gamma later began their invasion into the human world as part of the Demia Project, a plan to turn the human world into a mirror image of their own. The invasion was initially spearheaded by Alain until Adel killed their father and framed Alain for it, forcing Alain to go into hiding.
With Adonis out of the way, Adel became the new emperor of the Gamma and took over overseeing the Demia Project. Meanwhile, Igor brainwashed the board of Deep Connect in order to commandeer their resources for the Gamma's own ends. Adel aimed to create a utopia by becoming the world himself, allowing him to gain access to the Great Eye. To this end he fused with the Gammaizers to obtain the root of their power. Eventually, the Demia Project was completed, connecting the human world with Adel and turning everyone into copies of him.
However, Adel later turned his back on the Demia Project and attempted to renounce his evil ways, but the Gammaizers, having achieved sentience, fused with Adel to recreate Perfect Gammaizer. Though Perfect Gammaizer was later defeated, the Gammaizers revived and fused with the Great Eye to create the Great Eyezer.
After the Great Eyezer was defeated by Kamen Rider Ghost, the Eyecon system was terminated, resulting in the Gamma returning to their human bodies. Alain and the Fukami siblings later returned to the Gamma World to rebuild it.