Chappy is a compact robotic squirrel functioning as a steadfast companion to the protagonist. Initially a biological squirrel, he was cybernetically rebuilt after surviving a spacecraft accident that left him stranded on a high-gravity alien world. These modifications endowed him with flight capability and technical expertise, allowing him to support interstellar missions through navigation and mechanical repairs.

Residing with an archaeologist’s family on Earth, he aids in locating the protagonist’s missing sibling while providing levity and optimism during tense moments. His dual role merges practical utility—mechanic, navigator—with emotional camaraderie, often diffusing stress through humor.

Chappy’s design history intersects with a plagiarism dispute: his concept purportedly resembled a character from an unreleased Osamu Tezuka manga, triggering the "Wonder Three incident." To avoid overlap, Tezuka reimagined his character as a rabbit, whereas Chappy retained his squirrel form. His mascot status was discontinued in 1967, replaced by a bird in later media.

Personality evaluations describe him as inventive and spirited, employing creative problem-solving and impulsive yet effective decisions. His narrative centers on adaptability and unwavering loyalty, with no official expansions beyond his defined role in existing lore.