Ken Washio is the designated leader and tactical expert of his team, known by the codename G-1 or Ken the Eagle. His civilian cover occupation is that of an aircraft test pilot, and he also works part-time delivering airmail and performing other odd jobs that require the use of a small plane. He lives in a small shack beside a private airstrip, on a few acres of land that were willed to him by his father.

Ken grew up believing his parents were dead. His father vanished when Ken was very young, leading him to assume he perished in a plane crash. His mother later died of an unspecified illness when he was eleven years old. Following her death, the scientist Dr. Kozaburo Nambu became his guardian and oversaw his training to become a member of the Science Ninja Team, which began when Ken was thirteen. In some story continuities, he also has a background as a military pilot, known as "The Star of Africa."

In terms of personality, Ken typically maintains a calm and collected demeanor. However, in high-stakes crises, he can become emotionally overwhelmed and swept up in his feelings, at which times he relies on his teammates for support. He is an avid reader who spends his leisure time with books. Despite his heroic nature, he has notable flaws; he is financially irresponsible, frequently accruing debts at a snack bar run by his teammate Jun and relying on the youngest member of the team to cover his expenses. He is also notably inept when it comes to romance, either being too focused on his duty or simply oblivious to the feelings of others, particularly Jun, who has romantic feelings for him.

Ken’s primary motivation is to restore peace to the world by fighting the terrorist organization known as Galactor. For a time, he also fights to avenge his father’s death. A pivotal moment in his development occurs when he learns that the mysterious ally known as Red Impulse is actually his father, Kentaro Washio, who had faked his own death to go undercover within Galactor. Their reunion is tragic, as his father immediately sacrifices himself to destroy a Galactor missile. This loss plunges Ken into a deep depression, but he eventually emerges from it with a renewed and more resolute determination to destroy Galactor. In later storylines, he suffers from cellular degeneration as a side effect of using a powerful special move with his team's mecha, a condition that deteriorates his health over time.

As the team leader and tactical expert, Ken’s role is to coordinate his teammates during missions and command their combined mecha, which he pilots as the front section. His primary weapon is the Birdrang, a rocket-powered boomerang with extendable blades that can strike an opponent on both its outward and return path. He is proficient in multiple martial arts, including judo, karate, kendo, kobudo, and aikido, and integrates kickboxing and boxing into his combat style. His fighting style emphasizes speed and agility. He also employs Science Ninja Techniques, including the Bird Flash, which releases a blinding light to disorient foes, and a technique that uses holographic projection to create solid doubles of himself.

Key relationships define his character arc. His dynamic with his second-in-command, Joe Asakura, is central; their opposing personalities often lead to clashes, but they share a deep mutual respect, trust, and a strong bond as core teammates forged through their shared upbringing under Dr. Nambu. He sees his teammate Jun as a respectable and trustworthy ally, though he is largely unaware of or unable to reciprocate her romantic interest in the original series, a dynamic that evolves in later adaptations. Dr. Nambu serves as his mentor and a father figure who raised and trained him. The burden of leadership, particularly following the loss of his father and the sacrifices of his friends, weighs heavily on him and shapes his development into a more driven, and at times darker, character as his story progresses.