In the 2003 anime series often referred to as "Little Astro Boy," the protagonist is a young robot boy named Astro. His creation stems from tragedy, as he was originally built by the brilliant but grief-stricken scientist Dr. Tenma to replace his deceased human son, Tobio. Possessing the most advanced artificial intelligence ever created and an atomic-powered engine, Astro was designed to be a perfect replica. However, because Astro could not grow or age like a real child, Dr. Tenma ultimately rejected him, shut him down, and abandoned him.

Astro's story truly begins when he is discovered and reactivated by Dr. O'Shay, the kind-hearted new head of the Ministry of Science. Dr. O'Shay becomes Astro's mentor and adoptive father figure, providing him with a home, enrolling him in school, and even creating a robot family for him, including a sister named Zoran. This sets the stage for Astro's central struggle: navigating life as a powerful robot trying to find his place in a human world.

In terms of personality, Astro is defined by his powerful sense of justice, compassion, and unwavering optimism. He is brave, selfless, and deeply believes that robots and humans can and should coexist as friends. This belief is his primary motivation, driving him to act as a reluctant superhero who defends both humans and robots from various threats. Unlike many other robots, Astro possesses a quality called "kokoro," a Japanese term for heart or mind, which allows him to experience the full range of human emotions like joy, sadness, and empathy. He is clever, resourceful, and often tries to reason with his adversaries before resorting to force.

Astro's role in the story is that of a bridge between two conflicting worlds. He frequently finds himself caught between anti-robot factions that view machines as dangerous tools and robot uprisings demanding freedom from human oppression. As a robot who feels human emotions and fights for justice, he is a unique and often solitary champion. His key relationships are central to the narrative. His bond with his creator, Dr. Tenma, is complex; Tenma evolves into a primary antagonist who believes robots are superior and wants Astro to lead them, creating a painful conflict for the boy who only seeks peace. In contrast, Dr. O'Shay provides unconditional support and wisdom, always advocating for Astro and the cause of robot-human friendship. At school, Astro forms friendships with human children, though he is sometimes resented for being a robot, which adds to his experiences of discrimination and isolation.

Throughout the series, Astro undergoes significant development. He begins his new life trying to emulate a normal human boy but is constantly pulled away by his heroic duties. He struggles with his own identity, questioning what it means to be a robot built in the image of a dead child. As he faces escalating conflicts between humans and robots, his initial idealism is tested, forcing him to mature and find more nuanced solutions to deep-seated prejudice and hatred. His journey is not just about fighting villains but about forging his own identity and purpose, separate from the son he was meant to replace.

Astro's notable abilities are extensive and make him a formidable force. His most iconic power is his ability to fly at extreme speeds using the jet-rockets concealed in his arms and feet. He possesses immense superhuman strength, often cited as 100,000 horsepower, which can be boosted to one million. He is armed with various weapons, including lasers in his fingers and a powerful arm cannon, which is a notable addition in this 2003 version. His artificial brain grants him extraordinary analytical skills, the ability to speak thousands of languages, solve complex math problems instantly, and possess super-sensitive hearing. He also has searchlights in his eyes and, in some interpretations, the power to see into a person's heart to determine their true intentions. These powers, combined with his human-like heart, make him a truly unique and incorruptible hero.