Jimmy Sparks is a young boy, typically described as being twelve years old, who serves as the central protagonist and the designated controller of the giant robot Gigantor. He is the son of the late Dr. Sparks, the original creator of the immense robot. Living in the futuristic setting of the year 2000, Jimmy resides on a remote island alongside his uncle, Dr. Bob Brilliant. His upbringing in this unique environment contributes to a lifestyle that is far from ordinary for a boy his age; he is often seen wearing shorts and a jacket and is known to carry a sidearm. Demonstrating a remarkable level of independence and capability, he is also occasionally depicted driving a car despite his youth.

In terms of personality, Jimmy Sparks is characterized by his eagerness to help others and his unwavering determination in the face of danger. He approaches his responsibilities with a serious and fearless attitude, acting as a competent and resourceful boy detective. When a friend or innocent people are in peril, Jimmy mobilizes quickly, showing a deep sense of duty to use Gigantor's power for the protection of peace rather than for destruction. His motivations are rooted in honoring his father's legacy by ensuring that the robotic technology is used as a force for good, actively working to thwart the schemes of various villains and criminal organizations who seek to steal or weaponize advanced robotics for evil purposes.

Within the story, Jimmy Sparks's primary role is that of Gigantor's operator. The robot possesses incredible strength and flight capabilities but has no intelligence of its own, meaning it is entirely dependent on Jimmy's commands via a remote control to take any action. This makes Jimmy the crucial link between the machine's immense power and the fight for justice. He is not merely a passive observer but an active participant in the adventures, often facing danger directly. His key relationships include his deep emotional attachment to the robot Gigantor, whom he controls, and his living situation with his uncle, Dr. Bob Brilliant. He also comes to the aid of allies, such as the scientist Dr. Derek Conner, demonstrating a network of friendships built on trust and mutual assistance in the scientific and crime-fighting communities.

Throughout his adventures, Jimmy Sparks shows a capacity for growth as he faces increasingly treacherous challenges. His resolve is tested through mysterious revelations and unexpected twists, forcing him to employ strategic thinking and quick reflexes alongside Gigantor's raw power. While not possessing any superhuman abilities, his notable skills include his proficiency in operating Gigantor's remote control, his sharp instincts as a young detective, and his remarkable courage in confronting dangerous adversaries. He is defined by the values of bravery, friendship, and an unyielding commitment to fighting for what is right, embodying the responsible steward of a power that could otherwise threaten the world.