AppearanceZoro is a muscular man. He is almost always seen carrying around his three swords, usually bundled up with his green sash (or haramaki) over his right hip, which is favorable so he could easily draw any one of them with his left hand; his right hand is usually seen resting over the swords. This may indicate that he is left-handed or even ambidextrous, for most sword wielding characters in the One Piece Universe wear their swords on the left. On his left ear he wears three earrings and he normally has a bandanna tied around his left arm that he ties around his head when he is fighting seriously. The rest of his clothes vary from time to time; however, he usually wears a white shirt, dark green trousers, black shoes and the green haramaki sash around his waist.
His body is covered with scars from his many battles- during the Baratie Arc he lost a duel with the world's greatest swordsman, Mihawk, and was left with a massive scar across his torso. In the Little Garden Arc he tried to free himself from a wax prison by cutting off his feet. Although he did not entirely succeed, he gave himself a scar around each ankle. These scars are marked by black stitches
His other remarkable feature is his green hair, which Sanji often teases him about, calling him 'marimo' (moss-ball, moss-head in the Viz Manga and FUNimation dub).
According to Oda, Zoro resembles a shark. Oda uses the color green to represent Zoro, and he smells of steel.
PersonalityZoro usually maintains a stern, serious and distanced personality, but often loses his temper in a goofy and exaggerated comic style. He has a strong sense of reason when it comes to actual leadership of the crew and will often point out the seriousness of situations (such as Usopp's leaving the crew). And while technically not a samurai, Zoro maintains Bushido to a certain degree (i.e. he consistently refuses to attack an adversary whose back is turned on him, and neither does he tolerate getting assaulted from behind himself except when his crew mate is really in dire situation of dying of from an enemy threat, such as Kuma trying to take Luffy away, Zoro silently attacked him with Shishi Sonson) and is constantly mistaken for one. Whether he agrees with them or not, he will stand by Luffy's decisions, stepping in only to voice an opinion when the others have failed to see the true reality of a situation (again, such as Usopp rejoining the crew). He, like Luffy, has a lousy sense of direction (possibly even worse than Luffy's, since he usually assumes the others have gotten lost, and not the other way around). He is teased often because of it.
When the crew sails from one island to another, he normally either trains with weights or just sleeps and is normally awakened in a rather violent way by either Nami, Sanji and (accidentally) Luffy. His only apparent job on-board the Going Merry was using his enormous strength to haul up the anchor. Aboard the Thousand Sunny, however, he has been shown to seemingly spend most his time in the Crow's Nest (which is also a gym), so it is possible that he was designated as the ship's lookout. He also likes sake, almost to the degree that Luffy likes meat, but like Nami, he mostly never gets drunk due to his inhumanly-high tolerance for alcohol. He is sometimes prone to using serious methods for solving simple problems such as separating him and Usopp from cuffs by suggesting to cut off a hand, and cutting off his feet to get himself unstuck from some wax.
Zoro can also be very vigorous and won't back down when he is determined to achieve a goal or defeat an enemy. The risks that Zoro will often take to reach his dream of becoming the best swordsman often leaves others wondering if he is crazy. As far as Zoro is concerned though, only he has the right to call himself "Crazy".  However, he is not one who stubbornly refuses utter defeat, especially if it all seems so inevitable. When Zoro has the intention to fight seriously, he normally ties his black bandanna (which is usually tied around his left upper arm) over his head. Furthermore, like any great warrior, Zoro is one who lives for the thrill of combat; in fact, he has a habit of showing a joyful smile whenever he faces a particularly skilled opponent, which often unnerves both ally and foe alike.
Also, Zoro can provide important and logical decisions at critical times by evaluating the situation, as he did when the crew wanted to bring back Usopp in the Enies Lobby arc. Zoro is the one who mentioned that Usopp is at fault for leaving the crew on his own accord, and Luffy shouldn't take him back unless he apologizes for his mistake.
He also is one of the first Straw Hat members to suggest killing someone or threatening to kill someone.
CrewZoro trusts Luffy implicitly, and always goes for his decisions whatever the consequences, acknowledging it as a captain's decision, which a crew must carry out without questioning. Zoro likes to compete with Sanji and they often get into fights over petty matters, often at inopportune moments. However, when the pair fight together against a common foe, they're a nearly unstoppable team. Despite their comical fights and rivalry, they have a brotherly trust and care between them they`d never admit to. Both Usopp and Chopper are in total awe of his strength and 'tough-guy' attitude. He also appears to have a close relationship with Chopper, seeing as the youngest crew member runs to him when he is scared or in danger, and the swordsmen is the first one to jump into action whenever Chopper falls in the water. Owing to his simple, direct nature, he is often exploited by the more cunning Nami, particularly in financial matters. After Arabasta, when Robin joins the crew, Zoro didn't trust her, but later grows to trust her. Since Brook's entrance into the crew, he and Zoro have a sort of respect towards one another perhaps for both being swordsmen.
FriendsBefore the storyline, Zoro had traveled around with two training partners, Johnny and Yosaku whom called him "Aniki" (older brother). He seemed to share a good relationship with them as a group of traveling bounty hunters. When they last saw each other, Zoro parted with them on good terms; however, they acknowledge that as a criminal they cannot be seen with him.
He was also child-hood friends with Kuina. He never beat her but, after they made a promise, she died. He holds his vow to Kuina dearly and whenever he comes close to defeat (such as the events with Morgan and Mihawk), he recalls her memory and his promise to spur him on.
EnemiesHe lacks Luffy's trust in others, thus he is often overly cautious when dealing with certain people. But usually, he will resort to intimidation when it comes to most situations, causing others (usually people much weaker than him) to react with complete fear. Zoro has a habit of making many more enemies wherever the crew ventures when compared to any other Straw Hat.
Zoro has a unique relationship with Ensign Tashigi of the Marines. Tashigi and Zoro met in Loguetown, where she helped him search for a new katana. Zoro defeated her once when she attacked him after finding out that he was a pirate, but refused to fight her again in later confrontations due to her uncanny resemblance to his childhood friend, Kuina. So far, whenever he has seen her, he has run away claiming that she is the one person he cannot fight.
During his journey, Zoro has also made or met many rival swordsmen such as Mihawk, Hatchan, Mr. 1, Priest Ohm, Kaku and Samurai Ryuuma.
Abilities and PowersZoro is considered to be one of the Straw Hat crew's top three fighters; so much that people occasionally mistake him as the captain of the Straw Hat Crew after witnessing his fighting skills in battle. Mainly, while Luffy always fights the most powerful enemy, Zoro always fights the second strongest. Even without his swords, he has monstrous strength. He is able to toss an entire building at an opponent and even able to deflect Oars' punch singlehandedly. He can use some sword techniques without his swords. Zoro has shown to pack powerful punches. He even developed the ability to pump his arms up with pure muscle.
Zoro is unarguably one of the strongest characters revealed thus far. While most super powered pirates and villains gain power from eating one of the Devil Fruits, Zoro has gained his powers through hard work and training. Zoro has enough power in his lower body to allow him to keep up at a running pace with Sanji, who is a master of his own Leg-based style. He can also move at near-inconceivable speeds and jump astonishing heights. He can even dodge bullets with ease. He has been known to effectively knock out much larger creatures with unarmed strikes. Zoro also defeats opponents with massive punches and kicks. Also, during his fight with Kaku, he used an ability that gave him seemingly god-like powers. What this ability was, and how he attained it, are still unclear, but it was powerful enough to make numerous holes in the ground, as well as defeating Kaku. In Enies Lobby Arc, the Franky Family and Galley-La carpenters noted twice that Zoro was strong enough to be the captain of the group.
To match his strength, Zoro also has ridiculous amounts of stamina and endurance. Some of the things Zoro has endured include Mr.1's two buzzsaws jamming into his chest during the Arabasta arc, Arlong's saw-like nose stabbing into his face, Mihawk's Black Sword slashing his chest, CP9's Kaku's many Rankyaku attacks, and Kuma's Ursus Shock. Zoro managed to stay conscious while everyone else was incapacitated. Zoro then convinced the Shichibukai to transfer all of Luffy's pain and fatigue into him. Kuma was confident Zoro wouldn't live. However, the swordsman was seen standing blood-drenched at the end of the chapter/episode, claiming that nothing happened.
During almost all of his major battles, Zoro is usually seen covered with blood at the end (Oda has stated that Zoro lost 5 liters of blood fighting Hachi and Arlong at Arlong Park [It should also be noted that the human body holds about 8 liters of blood]). Zoro's agility, speed, and overall reflexes are also extraordinary. In numerous occasions, Zoro has shown being able to evade (or block) high-speed attacks and projectiles. These high-speed attacks and projectiles move so fast that it would normally be impossible for an average human to even notice them, much less evade them.
A running gag throughout the series is that while he is very perceptive during battle (as well as out), his sense of direction is extremely poor, to the point of getting lost on a straight path. This is often the result of Zoro not understanding directions. In the Arabasta Arc, he mistakes going north for going up. In the Drum Island Arc, he believes that he can keep the ship on course by heading toward a large cloud (which can move and change shape). He is unaware of his lack of direction. Everytime he gets lost, he mutters "the others are lost again". This is further made fun of with Jigoro in Thriller Bark. Jigoro had Zoro's shadow implanted in him. While the Zombie Generals were heading to help, he goes in the opposite direction. However, Zoro has other strong senses and is often one of the first members of the crew to hear an enemy approaching or sense danger.
Unlike some of the members of the crew, Zoro does not shrink from the idea of using deadly force against dangerous enemies.
WeaponsZoro is a master swordsman, being able to use one, two, and three swords in varying attack styles, going from melee-type all the way to artillery. Although he is most comfortable with his Santōryū (literally: three sword style), his skills with a single sword are very good, being able to hold off the Nyaban brothers, having bested several of the lower-ranked members of Arlong's crew (his two other swords were destroyed by Mihawk, leaving him only with the Wado Ichimonji), defeating Mr. 1, and most recently the zombie, Ryuuma. Lacking a third hand for a third sword, Zoro holds his third sword in his mouth. Some of his sword techniques use the air itself to hurt the enemy. Zoro often speaks with his sword held in his mouth, though it's unknown how he manages to do so. The creator of the series, Eiichiro Oda, has said that it is his heart that allows him to speak, though Oda is known for giving joke answers to fans' questions, as well as just making up answers on the spot to avoid leaving a fan's question unanswered.
Since no one else has been seen using anything similar, it can be assumed that Zoro invented not only Santōryū but most, if not all, of his sword techniques. He is even seen perfecting a new technique in his fight with Braham.
If he is fighting weaker enemies (or innocent bystanders that he has no desire injuring in the first place), like the Galley-La employees in Water 7, he uses only the blunt sides of his swords. Although, as Nami pointed out, due to his strength, even that could cause fatal wounds. A long standing problem with Zoro was his inability to cut steel. The anime incorrectly shows him instinctively cut steel during some of his encounters before learning how to control this ability during his battle with Daz Bones.
Zoro has shown a new ability called "Asura",
which gives him the appearance of having six arms and three heads, like the deity of the same name. The exact nature of this attack is currently unclear, but Kaku suggested it was an illusion created by Zoro's spirit. He cut through Kaku's attack, and was able to deliver the finishing blow.
Zoro using "Asura",with 6 arms,3 heads and 9 katanas
Though Brook became the crew's 2nd swordsman, the level of mastery and power between the two is significantly different, made obvious when both swordsmen have attempted to take on the same foe. While Brook had been unable to defeat Ryuuma (no matter how hard he fought) while Ryuuma only used a fraction of his power, Zoro was able to defeat him at full power with only two of his swords. At the Sabaody Archipelago, Brook struck a Pacifista with a high speed sword attack, yet failed to do much damage to it and had to be rescued from this result afterwards. However, when Zoro attacked the same Pacifista, the results were very different.
Zoro's SwordsDuring his adventures, Zoro has acquired many swords. The three he currently uses are:
1. Meitou; Wadō Ichimonji (formerly belonged to Kuina)
2. Sandai Kitetsu (formerly belonged to Ippon-Matsu)
3. Meitou; Shuusui (formerly belonged to Ryuuma)
Former SwordsFor one reason or another, Zoro has one or more of his swords destroyed or incapacitated in some way:
1. Katana x2 (destroyed by Juracule Mihawk)
2. Johnny and Yosaku's swords (returned to them after battle)
3. Meitou; Hana Arashi (Sogeking handcuffed to Yubashiri, stopped using when Sogeking was unlocked from Zoro)
4. Meitou; Yubashiri (formerly belonged to Ippon-Matsu, destroyed on Enies Lobby by Shuu, now resting on Thriller Bark)
5. Marine cutlass (destroyed by Shuu)