Goemon Ishikawa XIII is the thirteenth generation in a line of renegade samurai and a direct descendant of the historical outlaw Ishikawa Goemon. First appearing as a formidable adversary in the original manga, his initial purpose was to protect his clan's secrets, and he made several attempts on the life of Arsène Lupin III. Over time, this rivalry transformed into respect, leading Goemon to become one of Lupin's most loyal and trusted associates, though he typically joins heists on a selective basis when his personal interest or moral code is engaged.

Personality-wise, Goemon embodies the archetype of the stoic and dedicated warrior. He is famous for his calm, collected demeanor and his unwavering commitment to the way of the samurai. Despite his loyalty to the gang, he is frequently exasperated by Lupin's reckless antics and infatuation with women, particularly the treacherous Fujiko Mine, whom he distrusts due to her exploitative nature. In contrast, he shares a much more amicable relationship with Daisuke Jigen, viewing him as a fellow honorable warrior and a trustworthy partner in the field. Goemon holds a deep sense of pride in his abilities and feels profound shame when he fails at a task or when his legendary sword, the Zantetsuken, is broken or dulled.

In the story of The Secret Page of Marco Polo, Goemon experiences a period of introspection regarding his lifelong devotion to the blade. This internal journey takes him deep into the mountains, where he unexpectedly finds romance, leading him to reconsider his solitary path as a swordsman. This subplot runs parallel to the main adventure involving Lupin, Jigen, and a lost treasure, culminating in a worldwide chase that blends historical mystery with personal discovery for the samurai.

Goemon's most notable ability is his peerless swordsmanship with the Zantetsuken, a blade so sharp it is reputed to be capable of cutting through virtually any physical substance, including steel, bullets, and even entire buildings. His signature catchphrase, uttered after he destroys an object rather than taking a life, is "Once again, I have cut a worthless object," reflecting his preference for incapacitating foes by destroying their weapons or clothing rather than killing them. Beyond his sword, Goemon adheres strictly to traditional Japanese culture in his daily life, wearing a kimono and hakama, eating only Japanese cuisine, and frequently practicing meditation. He also possesses a surprising naivety, particularly regarding beautiful women, which often lands him in trouble despite his otherwise formidable and disciplined nature.