Also known as the Pirate Hunter, and famed for his usage of the Santoryu in One Piece, Roronoa Zoro is the combatant of the Strawhat Pirates and is second to Luffy in terms of strength.
Zoro is the second-strongest member of the crew and that will most likely always be the case in the story. After defeating Kaido's strongest underling, King, Zoro was recognized as the strongest commander of the crew.
1 Dracule Mihawk
Dracule Mihawk is Zoro's biggest rival, being the man who holds the title of the World's Strongest Swordsman. Mihawk is extremely skilled with the blade and his swordplay is described as very aesthetic.
His training under Mihawk significantly increased his powers, but he still has a long way (the ones above him) to go to become the Greatest Swordsman, which he will likely become in the future. Zoro's defeat against Mihawk back then shaped him to become one of the strongest swordsmen currently.
Points: Zoro 1, Law 0 Devil Fruit Roronoa Zoro is a very powerful character. He is known as one of the most powerful characters in the series and one of the series' best swordsmen; he is, by all means, probably going to surpass even Mihawk in the future.
Eclipsing Zoro in both mastery of Armament and Conqueror's Haki, Luffy proves himself stronger than Zoro overall. While Zoro does edge out a victory in terms of strength and physical endurance, Armament and Conqueror's Haki are undoubtedly the two more relevant factors here.
Sadly enough, Zoro would have trouble fighting Naruto's most powerful Uchiha due to the Sharingan. Madara would avoid Zoro's attacks without even breaking a sweat, ending the fight only with a few hits.
Shimotsuki Ryuma was a legendary, world-famous samurai hailing from the Shimotsuki Family of Wano Country, who lived during Wano's "Country of Gold" era centuries ago. He was revered for his mastery of swordsmanship that earned him the title Sword God, as well as his feat of slaying a dragon.
Quite easily one of the toughest battles that Zoro has been in is the one that he fought against Dracule Mihawk, the man who currently holds the title of the World's Strongest Swordsman.
2) Zoro. Zoro's awakening of Advanced Conqueror's Haki solidified his place above the Straw Hat chef. Zoro has always been the second strongest member of the crew, a worthy title for the ship's vice-captain to hold.
Zoro isn't given the title of Vice-Captain because the Straw Hats don't have a hierarchy system. They only have a Captain, and the others have specific roles assigned to them, such as chef, navigator, doctor, etc. The Straw Hats are an unorthodox pirate crew in the series.
Mortician: Sasuke was also way faster, Zoro was fast enough to keep with the teleporting Former King of Sorbet Bartholomew Kuma.
He can now use an advanced form of Conqueror's Haki to infuse his swords with great power, but even this ability cannot beat Naruto. Sage Mode would make landing a sword strike very difficult, and it is hard to believe that Zoro would be able to cut through Naruto's Tailed Beast Mode.
Kakashi might be able to keep up with a swordsman who uses a conventional fighting style, but it will be a bit difficult to deal with Zoro who can cut a building in half with a single swing.
One of Zoro's most prominent weaknesses is his utter inability to follow directions, resulting in him frequently getting lost. He only became a bounty hunter after leaving Shimotsuki Village because he lost his way while out at sea looking for Mihawk.
Shanks is probably way above Zoro`s level. Of all the characters still alive in One Piece, Dracule Mihawk is undoubtedly the strongest swordsman in the world. After all, he holds the title. Vista was the commander of the fifth division of Whitebeard`s Pirates and was considered the best swordsman in Whitebeard`s crew.
The fight is, undoubtedly, the most difficult one that Luffy has fought so far. Kaido managed to defeat Luffy three times. For the first time, Luffy faced defeat against him Kuri and was thrown in prison. There, he learned Internal Destruction Ryuo and took Kaido on during the Onigashima Raid.