Luffy seems to have an unstoppable appetite, a characteristic that is common to the Japanese archetype of the (at times simple-minded) young male hero/adventurer with a heart of gold; perhaps the hunger more so in Luffy's case due to having an elastic stomach. Luffy is also another one of the several characters given the middle initial "D." Although Luffy is fairly lightheaded and a funny character, he has an unstoppable sense of determination, optimism, and commitment and will do anything to stand up for his friends and comrades. Along with that, he has great courage to back it up as well as unbelievable strength. Ever since consuming the devil fruit he was shown to be not worried about his inability to swim, much like his brother. Much of these traits are common among D's. His only display of true fear is towards his grandfather, to the point that he is intimidated at the mere mention of him. Luffy never kills any of his enemies, no matter how cold-hearted they are; instead, he frequently sends the villain flying, knocking them out or beating them to a point that they are almost near death, which results in some of the villains searching for revenge, such as Buggy the Clown and Alvida. Oda explains that it's not a question of morality so much as a matter of punishing the villains for their crimes - he feels that killing the villains lets them off too lightly, whereas he considers letting them live to see their dreams be ruined a far more fitting punishment. Luffy's dream is to find the One Piece and become Pirate King. He knows that to achieve his goal, he will have to defeat many strong opponents, including the World Government and his childhood hero Shanks.

Though not a samurai, he appears to maintain a certain degree of bushido, and is frequently mistaken for one. Unlike Luffy and most of the other Straw Hat pirates, Zoro has been known to kill his opponents if he has to, though never in cold blood. Zoro has a stern, serious and distanced personality, but, unlike Robin, he often reacts in a goofy and exaggerated comic style due to his gruff, impatient attitude. On the ship, he normally either trains with weights or sleeps. The only work he is seen doing regularly is hoisting the anchor using his great strength. He also likes sake, almost to the degree that Luffy likes meat, but like Nami, he never gets drunk due to his inhumanly-high endurance and tolerance for alcohol. Another notable trait is his lack of orientation, as Zoro often gets lost, even in small, familiar spaces or when being led by someone. Despite this, he is often the first to sense an enemy or danger, and the first to react. He is often displayed being well aware of dangerous situations and people around him. Zoro often also reminds others of the harsh facts, which often shocks some of the other crew members, although they usually decide he is right. Zoro has also stated that he is an atheist, and has never believed in anything except himself. He often comes across as arrogant and overconfident, but only because he knows he's a strong man with great fighting ability. Even so, Zoro knows that he still has a lot of untapped potential, and is constantly seen training and trying to improve his fighting skills. He also adheres to a strict sword master's code of honor, and never falsely brags or lies about his abilities, sometimes outright admitting a weakness, even to an enemy. He also never tries to escape from a fight or use trickery to win, believing that doing so is cowardly and scorning anyone who uses such tactics. Zoro is very vigorous, strong-willed, and determined.