Eikingu is a kaijin, a monster created by the secret criminal organization known as Shocker. This character appears in the 1972 film Kamen Rider tai Jigoku Taishi, which translates to Kamen Rider vs. Ambassador Hell, as well as in the original Kamen Rider television series from the early 1970s. His design and abilities are based on a stingray, specifically the electric ray, and he is sometimes referred to as the Lightning Monster.

The background of Eikingu is that he is a biological weapon engineered by Shocker to carry out its plans for world domination. His creation involves the fusion of a human with the genetic traits of a stingray, granting him a unique set of superhuman powers. In his monstrous form, he stands approximately 195 centimeters tall and weighs around 90 kilograms. He is recognized as an exceptionally powerful monster; one of the main heroes once described him as the most formidable kaijin he had ever faced up to that point.

Regarding his personality and motivations, Eikingu is depicted as a loyal and dangerous operative of Shocker. He is a combatant who follows the orders of his commanders without hesitation. His primary mission in the television series is to participate in the World Darkening Operation, a scheme designed to destroy power plants in major cities across the globe, plunging them into chaos. He is also shown undertaking tasks such as attempting to recapture a fugitive who escaped from a Shocker outpost.

In the story, Eikingu serves as a major obstacle for the protagonists. During his initial appearance, his search for the fugitive leads him to cross paths with the Tachibana Racing Club, a group of allies who support the heroes. His role in the film Kamen Rider tai Jigoku Taishi is as a member of a revived monster army. In this movie, the villain Ambassador Hell sends a group of previously defeated Shocker monsters to eliminate the heroes, and Eikingu is among this resurrected force. He is shown participating in an ambush against Kamen Rider 1, one of the primary heroes, and his ally Taki, to buy time for another Shocker operation.

Key relationships for Eikingu are primarily with his superiors and his enemies. He serves under the highest-ranking members of Shocker, including Ambassador Hell to whom he reports directly in the film. He fights against the two main Kamen Riders of that era. In the television series, he is ultimately destroyed by Kamen Rider 2, who defeats him with the Rider Kick finishing move. In the film, he is shown in combat against Kamen Rider 1. He is also depicted leading squads of Shocker's masked soldiers, known as Combatmen, who wear a distinctive stingray silhouette as their personal emblem to signify their unit.

Eikingu is not a character who undergoes development or a story arc; he is a classic monster-of-the-week figure. His primary function is to serve as a physical threat to be overcome by the hero. His significance comes from his power level and his role as a recurring visual in the franchise, making brief reappearances in later films and even in the opening sequence for the final season of the original television show.

The most notable aspect of Eikingu is his impressive set of abilities, all derived from his stingray nature. His primary power is the generation and projection of high-voltage electricity. He is capable of releasing discharges of up to one million volts from his body, which he can also fire as bolts of lightning powerful enough to instantly vaporize a human being. He can fly through the air thanks to his ray-like form, giving him a tactical advantage in combat. His left hand is shaped like a blade, which he likely uses as a cutting weapon in close-quarters fighting. Despite these formidable powers, Eikingu has one specific weakness: after discharging a powerful bolt of lightning, there is a brief instant where his body is devoid of electricity, leaving him vulnerable to counterattack.