Jack is a human resident of Alien City who begins as an information broker and wrestler. He transitions into an informant for the Science Special Search Party (SSSP), later operating unofficially as a field ally after receiving a specialized armored suit. Standing 188 cm tall and weighing 116 kg at 32 years old, a distinctive bracelet adorns his left wrist, requiring explicit permission for activation. His background reveals significant combat prowess, demonstrated by winning boxing matches against alien opponents, often emerging unscathed. Jack possesses extensive knowledge of alien languages and criminal networks, crucial for his information-gathering role. A key partnership forms with Red, a former arena champion alien he defeated, becoming a recurring element in his operations; Jack frequently translates Red's speech for others. Key developments mark his shift from informant to active participant. He orchestrates distractions at Edo's request to test Shinjiro Hayata's abilities, deploying Red in giant form to battle him. When the Ace Killer Squad attacks, Jack and Red reinforce the SSSP; Jack provides cover fire using a repeating laser and evacuates an injured ally. Subsequently, he kidnaps scientist Yapool, relocating to New York to develop new armored suits for impending threats. Later, alongside two other suited allies, he protects Rena Sayama during riots incited by the Star of Darkness. Though overwhelmed, they hold until reinforcements arrive. Jack later collaborates with Kotaro Higashi to investigate a Detroit murder case. After defeating a three-eyed creature, they confront Fred, an alien driven to violence by the xenophobic murder of his wife. Forced to execute Fred, Jack prevents Kotaro from attacking the applauding crowd, underscoring the complexities of human-alien relations. Witnessing children intervene during anti-alien mob violence restores their faith in humanity. They subsequently face the Zetton Core warrior Tyrant, whom Jack defeats using the Ultra Axe, a massive polearm teleported directly to him. His technological capabilities originate from the "Jack Suit" (ジャックスーツ), developed by Yapool during their New York operations. This armor features a retractable mask stored in the back armor and forearm compartments housing multiple weapons: a railgun, retractable swords, and an L-shaped energy beam resembling the Cinerama Shot. It generates a normally invisible forcefield. Jack later acquires the MAT Shoot (マットシュート), a back-mounted energy weapon requiring an external battery pack due to high power consumption, and the Ultra Axe (ウルトラアックス), used decisively against Tyrant. His design elements, including the bracelet and name, serve as intentional references to the classic Ultra Warrior Ultraman Jack. His physical appearance also evokes similarities to Hideki Go, that character's human host.