Derek Wildstar, known in the original Japanese version as Susumu Kodai, is the central protagonist of the Star Blazers series. At the age of eighteen when the first voyage begins, he serves as the tactical officer and later as the acting captain of the space battleship Argo, which is known as the Yamato in the original version. His background is defined by profound personal tragedy, as his parents were killed during a devastating bomb attack on his hometown of Kanagawa Prefecture carried out by the alien Gamilon forces. This loss drove him and his older brother, Alex Wildstar, to join the Earth Defense Forces.

Initially, Wildstar's personality is heavily shaped by grief and a burning desire for revenge against the Gamilons. He is described as impulsive and hot-headed, often clashing with his superiors and fellow crew members, particularly his close friend Mark Venture, over whether to prioritize combat or exploration. A significant source of his early anger is Captain Avatar, the commander of the Argo, whom Wildstar initially blames for the death of his brother Alex, who was presumed killed in action near Pluto. This resentment eventually fades as he comes to understand the Captain's wisdom and the heavy burdens of command. Through the guidance of Captain Avatar and his experiences on the long journey to Iscandar, his rash nature mellows, allowing him to develop into a more disciplined and responsible leader. He learns that there are more important things than fighting and begins to reconcile his trauma with his duty.

Wildstar's primary motivation evolves over the course of the story. While he begins fueled by a personal vendetta, his driving force transforms into a steadfast dedication to protecting humanity and saving Earth from destruction. The planet is slowly being rendered uninhabitable by radiation from the Gamilon bombs, creating a ticking clock for the Argo's mission. His role in the story is central, initially as the leader of the battle group and a pilot of the Cosmo Zero fighter. As Captain Avatar's health declines, Wildstar is promoted to acting captain and later assumes the formal rank of Captain, taking full command of the Argo in subsequent voyages against new threats such as the Comet Empire and the Bolar Federation.

His key relationships are essential to his development. The most significant is his romance with Nova Forrester, the ship's radar operator. Their bond deepens during the first voyage, forming a personal anchor for him amidst the chaos of war, and they are later engaged. His friendship with the ship's navigator, Mark Venture, provides him with consistent and reliable support throughout their service together. He also shares a complex relationship with the Gamilon leader, Leader Desslok. They begin as bitter enemies but eventually become uneasy allies, forcing Wildstar to confront his prejudices and the realities of interstellar politics.

Wildstar has notable abilities as a highly proficient pilot and a skilled tactical commander. He leads the elite Black Tiger fighter squadron and often participates directly in combat operations, demonstrating daring and bravery in the heat of battle. As a commander, his style emphasizes crew protection and mission completion, and he is known for his tactical adaptability in the face of advanced enemy technology. He continues to develop across multiple seasons and films, facing new challenges such as a mission to stabilize Earth's dying sun, political isolation upon returning home, and the struggle to balance his duty with his desire for a peaceful life with his family. In later stories, he is shown to have a daughter named Miyuki. His character arc is a journey from a boy consumed by revenge to a mature captain who carries the legacy of his fallen comrades and symbolizes enduring hope for humanity's future.