Here is everything you need to know about the most intelligent characters in One Piece.
Also part of the MADS research team, Caesar is responsible for discovering lineage factors and applying them to artificial Devil Fruits. He was successful, resulting in the creation of SAD gas and SMILE Fruits. These SMILEs are responsible for many of the transformations seen amongst the Beast Pirate crew members in One Piece.
The final (currently known) member of MADS, Judge, was also responsible for discovering lineage factors. Furthermore, he and his Germa 66 kingdom are the only group in the series currently known to be capable of cloning. Judge is brilliant, as well as being shrewd and tactile in battle areas.
Franky’s intelligence only grows during the time skip, an incredibly talented shipwright who even turns himself into a cyborg. He discovers Vegapunk’s old lab and various research documents and projects from which he studies and learns. These new skills and knowledge are seen on full display in post-time-skip One Piece.
Trafalgar D. Water Law
Commonly referred to as just Law, the captain of the Heart Pirates is also their doctor. The true mark of his intelligence comes from studying to become a doctor from near birth and curing himself of Amber Lead Syndrome.
While he did accomplish this with the help of the Op-Op Fruit, the process still requires an incredible amount of medical knowledge. Even more impressive is the young age at which Law possessed such knowledge and skill.
Being the last survivor of Ohara, Nico Robin possesses ancient knowledge and skills, which nearly no one else in the series does. Her intelligence primarily manifests in her role as an archaeologist, including reading Poneglyphs.
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The first “good guy” on the list, the resident Straw Hat doctor, is incredibly gifted. Chopper’s development of the Rumble Ball proves this, allowing him to expand his Devil Fruit power in ways other Zoans are unable to. His knowledge of medicine is impressive, thanks to his origins as seen in early One Piece and further research mid-time-skip.