Ken Izumi is the main protagonist of the 1974 anime series. He is a young boy, established to be ten years old and in the fifth grade, who lives an otherwise normal life with his family. His household includes his mother and father, his younger sister Caron, and a robotic companion named Barican, who is often described as looking like a robot dog. In his everyday activities, Ken attends school and is portrayed as being very interested in the advanced technology of his era.

In his normal state, Ken possesses a notably high level of physical strength for a child his age. He is capable of easily overpowering grown men and is highly skilled in various sports, including boxing, wrestling, American football, tennis, and baseball. This physical prowess is demonstrated when he delivers a fatal, single blow to a formidable alien boxer named Tiger M, a fighter who had supposedly killed thirteen professional boxers. Beyond his physical abilities, Ken also exhibits psychic powers on rare occasions, including exceptionally sharp hearing and vision, as well as the ability to communicate telepathically.

When danger arises from an alien threat known as the Durals or Juralians, Ken has the ability to transform into a heroic figure named Chargeman Ken. By striking a pose and shouting the phrase Charging Go, he dons a helmet with a resistant visor, jet shoes, and equips a ray gun known as the Alpha Gun. His transformation is said to be powered by light, requiring at least a small source of illumination to activate. In his transformed state, he can also summon a flying vehicle called the Sky Rod, which is capable of traveling through both space and underwater. He also possesses a Bidium belt around his waist that can be powered up to create a powerful typhoon to disorient and blow away his enemies.

Ken is depicted as a model hero in concept, but the extremely short runtime of each episode often leads to resolutions where his decision-making appears questionable. For instance, in one infamous episode, Ken determines that a bomb has been planted in the brain of an ally, Dr. Volga, and concludes that the best course of action is to drop the living doctor onto a pursuing alien spaceship, destroying them both. He then mourns the loss of Dr. Volga, despite having directly caused his death. This behavior has led to interpretations of the character as being ruthless or having sociopathic tendencies, particularly as he often seems to revel in eliminating his enemies, even when they are disguised as humans or are fleeing and pose no immediate threat. These characteristics are widely considered by fans to be unintentional on the part of the creators, a product of the show's low budget and pacing issues, rather than a deliberate character trait.

At home, his personality is also marked by a mean-spirited streak, as he frequently plays cruel pranks on his younger sister, Caron, and his robot companion, Barican. He is known to have specific weaknesses, including a susceptibility to pretty girls, which the alien Durals often exploit, and a strong dislike for tomato juice. In one episode, his family identifies an imposter pretending to be him because the imposter drinks tomato juice without complaint. His motivation for fighting is ostensibly to protect the innocent and eradicate the alien threat, but his actions are often driven by a simple and brutal efficiency in dispatching the villains. He is consistently victorious in his battles, rarely facing any serious challenge or injury, and the narrative never portrays him as being in the wrong for his more extreme actions. In adaptations outside the original anime, such as a manga version, Ken is portrayed as being older, more muscular, and a considerably more conventional and heroic character.