Detective Dolphin, legally known as Dozaemon Umino, is a detective for the Tokyo Metropolitan Police Department, assigned to the Kameari district. He specializes in maritime and water-related investigations, leveraging his expertise in aquatic environments to track and apprehend criminals.

His physical appearance is highly distinctive. He typically wears minimal attire, primarily a fundoshi (a traditional Japanese loincloth). The word 'MARINE' is prominently written across his forehead. His outfit also includes long socks, shoes, and a hat-like object depicting a palm tree atop an island, positioned on his bald head. He carries a pipe used specifically to summon dolphins when their assistance is needed in his investigations.

Professionally, he demonstrates strong analytical skills and a meticulous approach, particularly in forensic science and evidence collection. He is known for solving complex cases that challenge other detectives. Despite his serious profession, he exhibits notable quirks, including wearing a dolphin mask during investigations and incorporating dolphin-like vocalizations into his speech patterns.

His personality blends a reserved, serious demeanor with moments of eccentricity. He maintains a stoic disposition while investigating but engages in unique behaviors that set him apart from colleagues, such as his dolphin communication methods and mask usage. He adheres strictly to protocols and values order, reflecting a structured approach to his duties.