Mihawk is a world-famous pirate who currently holds the title of “Greatest Swordsman in the World”.
Part of Mihawk’s reputation as the most powerful master swordsman in the world is also due to his tremendous superhuman physical power and fortitude which supplements his mastery of swordsmanship. He possesses an immense amount of skill in battle and has exceptional eyesight.
The fact that Mihawk used to be a rival of one of the Yonko implies that Mihawk might be one of the strongest characters in the series. Infact he has been known to have frequently fought with Shanks when they were younger. Their battles were said to shake the whole of the Grand Line and Mihawk often sought Shanks out for duels. However, Mihawk lost interest in him after Shanks lost his left arm. Mihawk has remained unharmed thus far throughout the entire series.
Sengoku the Buddha was the Fleet Admiral of the Marines pre-timeskip, succeeding Kong and preceding Akainu.
Alongside Garp and Tsuru, Sengoku is one of the most powerful Marines of his generation. Even without his Devil Fruit powers, Sengoku has enormous strength, enough to effortlessly hold down an enraged Garp with only one hand.
Sengoku ate the “Hito Hito no Mi, Model: Daibutsu”, a rarer-than-Logia Mythical Zoan-class Devil Fruit which allows him to turn into giant, living, Buddha-like golden statue, gaining an extreme boost in strength to match his size.
In this form Sengoku can launch golden shock waves to cause heavy and widespread damage to the enemies.
“Dark King” Silvers Rayleigh is the former first mate of the Roger Pirates, known as the “Right Hand of the Pirate King”. He’s extremely powerful, easily one of the strongest characters introduced.
Shakky vouches for his strength by saying that he is “100 times stronger than all of you boys”, referring to the Eleven Supernovas.
Furthermore, when Garp was informed Rayleigh may be on Sabaody Archipelago, he told his men not to confront him, he reasoned that the Marines should not confront two legends, Whitebeard and Rayleigh at the same time.
Due to his phenomenal strength, he was able to fight Admiral Kizaru equally and he even managed to scratch the admiral. However, Rayleigh himself has admitted that he is not as young as he used to be, and can tire in battle. This may mean when he was in the prime of his strength he may have been even stronger than when he matched Kizaru, a true testament to his strength!
Rayleigh has tremendous physical strength despite his elderly age. He is powerful enough to kill several Sea Kings with his bare hands while swimming in the Calm Belt.
He is shown to possess great mastery of Haki, and made use of all three types while teaching Luffy about them.