Doctor Regan leads scientific efforts on planet S-1, developing technology to reverse severe environmental pollution threatening his world. His research successfully produced a solution capable of cleansing S-1's radiation-contaminated environment, offering hope for ecological recovery.

During a coup led by military commander Zeo Gattler, Gattler's forces invaded Doctor Regan's laboratory. They deliberately destroyed his anti-pollution research and equipment to eliminate alternatives to Gattler's plan of planetary invasion. Doctor Regan and his scientific team were killed during this assault. His assassination followed the murder of S-1's emperor, an act for which Gattler's forces framed Doctor Regan and his colleagues.

This event directly motivated his son, Marin Reigan, to oppose Gattler's regime. Doctor Regan's death represents the suppression of scientific solutions in favor of militaristic conquest. His legacy persists through Marin's actions on Earth and the revelation of S-1's origins.

A significant plot twist reveals S-1 is actually Earth's future. The environmental devastation on S-1 resulted from catastrophic weapons deployed by Gattler during his invasion of Earth. Doctor Regan's research, had it been implemented, could have prevented this cyclical apocalypse. His scientific insights are referenced when Earth later faces identical ecological collapse from polar ice cap melting and nuclear contamination triggered by the conflict.

In the film adaptation, Doctor Regan appears in flashbacks that reinforce his relationship with Marin and contextualize his murder. These sequences underscore his role in the protagonist's personal motivations and the broader thematic exploration of environmental responsibility.