Lt. Zero, originally known as Pukko in Japanese media, is a Lieutenant within the 4th Squad of the Galaxy Patrol. Sent to Earth by the Galactic Federation (or Galactic League), his mission is to assess if humanity's violent nature justifies planetary destruction via an anti-proton bomb.

Upon Earth arrival, Pukko camouflages himself as a duck, mirroring his teammates Bokko (rabbit) and Nokko (horse). His duck form features a distinctive Beatles or Moe Howard-inspired hairstyle. Personality-wise, he displays a short temper, scatterbrained tendencies, and initial contempt for Earthlings. He frequently demands immediate detonation of the anti-proton bomb upon witnessing human conflict, clashing with more tolerant teammates.

Despite his irritability, Pukko possesses technical expertise, sometimes drafting blueprints for equipment built by Nokko. His abilities include generating shockwaves with his wings, exhibiting unexpected physical strength in avian form, and proficiently playing the guitar—a hobby showcasing his appreciation for Earth's music despite general disdain for its inhabitants.

His character develops through interactions with Shinichi Hoshi (Kenny Carter in English dubs), a young boy who becomes the team's ally. While remaining the most skeptical of humanity's worth, Pukko consistently aids the team and protects Shinichi during missions. His rigid stance shifts after a pivotal Galactic Council judgment: ordered to destroy Earth, Pukko expects compliance, but Bokko's defiance and Shinichi's impassioned plea challenge him. Following the council's decision to delay judgment, Pukko expresses shame for his earlier hostility towards humans.

In the narrative's conclusion, he actively participates in transforming Bokko into a human girl to facilitate her desire to stay with Shinichi, an act demonstrating his evolved, albeit grudging, acceptance of human connections.