Umberto Mori served as captain of the United Earth emigrant spaceship Aratrum. His background included involvement in "Operation: Eternal Light" in 2039, where he acted as deputy captain of the attack submarine Gōten during the battle against Manda in the Strait of Dover. This engagement resulted in Manda's defeat and led to Mori's appointment as captain of the Aratrum nearly a decade later.

Mori appeared as an older, weathered man with gray hair, a gray beard, and grayish eyes. A distinct scar marked the area over his left eye, its origin unspecified. His personality demonstrated caution and skepticism, particularly evident during strategic decisions concerning Godzilla. He expressed reluctance to risk lives in military operations against the creature, emphasizing the value of the remaining human population. Following Godzilla Earth's devastating attack on United Earth forces, Mori authorized a 48-hour window to search for survivors before considering abandonment of Earth.

During the events surrounding Mechagodzilla City's fall, Mori displayed indecisiveness regarding disciplinary action against Haruo Sakaki. This hesitation occurred amidst increasing tensions and a subsequent Bilusaludo rebellion led by Halu-elu Dolu-do, who seized control of the Aratrum's power station. When the Exif and Bilusaludo factions debated abandoning Earth versus continuing the fight, Mori proposed a compromise: retreating to the Moon's orbit while deploying reconnaissance drones to search for survivors.

Mori's final moments occurred during King Ghidorah's manifestation. As the entity generated a singularity near the Aratrum, he attempted to activate the ship's thrusters at full power. This effort failed when steering commands went offline. Ghidorah subsequently attacked the vessel directly, resulting in a nuclear explosion that destroyed the Aratrum and killed Mori along with everyone aboard.