Arsenio Lupin, more commonly known as Lupin III, is the titular protagonist of the anime and manga franchise. He is the grandson of the fictional French gentleman thief Arsène Lupin, created by Maurice Leblanc, and continues his grandfather's legacy as a master thief operating on a global scale. While his ethnic origins are not definitively specified across different media, he is often presented as being of French or mixed French-Japanese heritage.

The personality of Lupin III is notably inconsistent between his original manga depiction and the more famous anime adaptations. In the original manga, Lupin is portrayed as a crude, remorseless, and sociopathic criminal capable of violence and murder. In contrast, the anime versions have softened him significantly, recasting him as a chivalrous, fun-loving gentleman thief who dislikes killing and often uses his skills to help those in need. This anime incarnation is typically a goofball and a self-proclaimed Casanova, though his actual success with women is erratic. Despite his playful and sometimes foolish demeanor, he possesses a brilliant mind that is constantly improvising and re-evaluating situations to pull off heists that seem impossible.

His primary motivation is the thrill of the heist itself rather than the value of the treasure. Lupin relishes the challenge of defeating complex security systems and will often discard his loot or give it away once he has proven he can steal it. He operates with a self-defined moral code, refusing to steal "honest money" and often targeting wealthy, prideful individuals or stopping criminals engaged in more violent activities. He has a particular soft spot for children and those who are victims of injustice.

Lupin's role in the story is defined by his relationships with a core group of associates. His closest partner is Daisuke Jigen, a sharp-shooting gunman, and his other loyal ally is Goemon Ishikawa XIII, a master swordsman. His dynamic with the femme fatale Fujiko Mine is complex; he is infatuated with her, but she regularly betrays him for personal gain, a vulnerability that consistently jeopardizes his plans. His primary antagonist is Inspector Koichi Zenigata of Interpol, who chases Lupin across the globe. Despite being enemies, the two share a deep mutual respect, often forming temporary alliances against greater threats, a relationship the creator described as a "human Tom and Jerry".

Across decades of media, Lupin has evolved from a ruthless criminal into a more heroic antihero, though core traits have remained consistent. He is fiercely loyal to his companions, often risking his life for Jigen, Goemon, or even the betraying Fujiko. This loyalty even extends to Zenigata, whom he considers a respected friend and rival. He is an adaptive and enduring trickster whose character generally avoids permanent development due to the franchise's episodic nature, though he continues to explore his grandfather's legacy in various films and specials.

Lupin possesses a wide array of notable abilities. He is a master of disguise and vocal mimicry, capable of flawlessly impersonating any man or woman after minimal observation, with his favorite disguise being that of Inspector Zenigata. He is incredibly agile, flexible, and possesses cat-like manual dexterity. His favored firearm is a Walther P38 pistol, of which he is an excellent marksman. He is also a formidable escape artist, a skilled safe-cracker, a talented driver and pilot, and an inventor of handy gadgets like explosive cigarettes and grappling-hook watches. While his strength is only average, his genius-level intellect, intuition, and encyclopedic knowledge of various sciences and history are his greatest assets.