Ryukuman is an adult resident of the Rilulu alien village, established on Earth after a spaceship crash. He possesses wisdom and a mysterious nature, frequently dispensing advice to the village's younger inhabitants. His behavior involves spending extended periods alone, often sleeping beneath trees, and adhering to an unconventional lifestyle rhythm. Ryukuman maintains a generally kind and approachable demeanor toward the village children, establishing him as a trusted mentor figure within the community.

Alternative romanizations of his name include "Ryukkuman," "Leguman," and "Luckman," reflecting variations in subtitle translations. The name "Ryukuman" translates to a concept similar to "Backpack man" in Japanese, though the significance of this naming convention is not elaborated. His background prior to the spaceship crash and specific developmental arcs across media are not documented.