Roronoa Zoro, also known as "Pirate Hunter" Zoro, is the combatant of the Straw Hat Pirates, one of their two swordsmen and one of the Senior Officers of the Straw Hat Grand Fleet. Formerly a bounty hunter,[ he is the second member of Luffy's crew and the first to join it, doing so in the Romance Dawn Arc. As a master of Three Sword Style, a swordsmanship style which he created during his childhood training in Shimotsuki Village, Zoro is among the three most powerful combatants of the Straw Hats, alongside Luffy and Sanji] His dream is to become the greatest swordsman in the world, in order to honor a promise he made to his deceased childhood friend Kuina. In addition to his infamy as one of the Straw Hats and as a former bounty hunter, Zoro is also regarded as one of twelve pirates who are referred to as the "Worst Generation". He first gained a bounty of Beli.png60,000,000 after the Arabasta Arc. It later increased to Beli.png120,000,000 after the raid on Enies Lobby, then to Beli.png320,000,000 after the Dressrosa Arc. Following the Raid on Onigashima, his bounty was increased to Beli.png1,111,000,000..

Zoro is confident but often acts in a very comical manner. A running gag is that he has a terrible sense of direction (being capable of getting lost even while walking in a straight line) which he is very insecure about since he never admits when he gets lost, instead always blaming someone else. While the crew is out at sea, Zoro can (usually) be found sleeping or training towards his goal of becoming the world's best swordsman. He and Sanji have a great rivalry, often resorting to fighting (both verbally and physically) over issues from minor to extreme. Zoro had never called Sanji by his name in the original Japanese manga, he uses phrases like "dumb-cook", etc. On the other side, Sanji uses phrases like marimo (moss-head). etc. 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. It is shown that Zoro enjoys fighting a strong opponent (usually left to face down the second strongest villain in each arc, as Luffy faces down the strongest). Zoro tends to retain a maniacal grin and serious glare when battling a worthy opponent.

Zoro is uniquely known as an expert of Santōryū (Three Sword Style), where he wields a third sword with his mouth in combat. Throughout the series, his primary sword is Wado Ichimonji, one of the World's 21 great swords inherited from a childhood friend Kuina, and is frequently the sword he wields in his mouth, while the other two swords frequently change and improve over time. He is proficient in Armament and Observation Haki, as well as one of the few known characters who possess Conquerors Haki. During his battle against King, Zoro unlocks an advanced form of Conquerors Haki (Called Infusion), which gave him the ability to coat his swords with it, similar to Armament Haki, which could further enhance his attacks. He also uses an advanced form of Armament Haki (Called Emission) to shoot a short blast of Haki from a distance.