Rune is the son of Leo, the white lion emperor, and his mate Lyra (also known as Laiya or Leah). Born in the jungle, he starts as a timid and easily frightened cub struggling to live up to his father's expectations, but matures into a courageous and adventurous leader, reflecting Leo's qualities while retaining his own distinct traits. Physically, Rune closely resembles Leo in most depictions, with white fur, brown eyes, and distinctive black ear-tip markings. An exception occurs in the original manga, where he lacks ear markings and resembles his grandfather Panja more closely. His growth involves overcoming early fears to become a proactive jungle protector. Driven by intense curiosity about human civilization, Rune ignores warnings and travels to the African coastline. There, he is deceived into signing a contract with showman Adam Dandy. Transported to New York, he endures ten months of exploitative circus captivity. Rune resists humiliating treatment and orchestrates an escape during a fire caused by Acetylene Lamp, returning to the jungle by floating across the ocean on a log. Within the jungle, Rune participates in significant events: assisting Leo in ending a drought, confronting crocodiles and poachers, and helping build a unified animal kingdom. He faces recurring bullying from the elephant Bizo but consistently demonstrates bravery, including rescuing Leo and Dr. Mustache (Higeoyaji) from Mount Moon. The 1997 film reinforces Rune's reckless curiosity, depicting attempts to fly and explorations of a crashed airplane. His human encounter similarly leads to circus captivity, where he interacts with Mary and a mouse named Jack. Across all narratives, Rune's story culminates in him assuming leadership of the jungle. The original manga concludes with him mating with a lioness and fathering three cubs, establishing his legacy as the jungle's new protector. His name derives from reversing the syllables of the Japanese word "Neru" (寝る, "to sleep"), with the alternate transliteration "Lune" meaning "moon" in French.