Sabo is the Revolutionary Army’s chief of staff, recognized as the “No. 2” of the entire organization, ranking directly under Monkey D. Dragon himself.
After joining the Revolutionary Army, Sabo was personally trained by Monkey D. Dragon and attained tremendous physical prowess by adulthood.
Sabo ate the Mera Mera no Mi, which originally belonged to his brother Ace before his death. With it, Sabo is able to become the element of fire and control the flames from his body at will.
He can utilize and has shown mastery over two types of Haki: Armament Haki and Observation Haki.
Sabo could fight on equal level with Fujitora, a Marine Admiral and an immensely powerful swordsman, and emerged with only a few bruises. Later, Sabo single-handedly defeat Burgess, an immensely powerful wrestler who is one of the most powerful members of the Blackbeard Pirates with only minimal effort.
9-MARCO THE PHOENIX
Marco the Phoenix is one of the strongest characters in the entire One Piece series, as he demonstrated in the war that he was on a similar level of fighting as the three admirals and even Whitebeard himself.
Marco ate the Tori Tori no Mi, Model: Phoenix, a mythical Zoan-type of Devil Fruit which allows him to transform into a phoenix. It is an immensely powerful type of Zoan Devil Fruit, said to be the rarest type, even rarer than Logia fruits. The additional powers this devil fruit grants may be considered similar to those of Paramecia (the somewhat “superhuman” power that affects the user’s body: regeneration) and Logia (the generation of blue phoenix flames).
The fruit’s greatest attribute, however, is that Marco can recover from any damage he accumulates in his human form by reverting to his phoenix, or hybrid phoenix form, or just by summoning blue flames around his body.
Marco is also capable of using Haki proficiently.
Lucky Roo is one of Yonko Shanks’ most important men. He’s the first person to kill someone both in the anime and the manga, by shooting a mountain bandit in the head at point blank range.
During Romance Dawn, we see one of Higuma’s men pointing a gun at Shanks’ head, then after Shanks warns him suddenly Lucky Roo appears and shoots him. Now here’s the question, how can a big man like that go there that quickly without being noticed? It is likely that he is based on Lucky Luke (a fictional cowboy -gunfighter- from the “Lucky Luke” Franco-Belgian comic book) that is known as “The man who shoots faster than his shadow”.
Lucky Roo he’s supposed to be a Haki master or, anyway, a master in something different; in particular, many speculated that he uses a technique called “Life Return”. In this case, Lucky Roo eats so much because he is storing energy for a battle. Life Return gives him the ability to control his body; this can be used to turn fat into muscle, or just turn fat into energy.
Benn Beckman has the highest IQ of anyone in the East Blue. Since he is a first mate to a Yonko, he presumably possesses a great deal of strength. During the Battle of Marineford, Admiral Kizaru chose not to fight him, even though he had just fought the First Commander of Whitebeard’s crew and Whitebeard himself. When the Red Hair Pirates arrived at Marineford to stop the war, Beckman was able to climb on to a Marine ship’s mast and sit on it, all the while pointing his flintlock at Kizaru, without the latter noticing.
I would say he is a master in Busoshoku Haki and uses that rifle (armament the bullets) as both a ranged weapon and used as a club.
Kuzan, better known by his epithet Aokiji, is a former Marine admiral. After the time-skip, he became affiliated with the Blackbeard Pirates.
Kuzan has the powers of the Hie Hie no Mi, a Logia Devil Fruit that allows him to control, create, and become ice. He can create enough ice to cover a giant, a Sea King or several square miles of ocean within mere moments.
This fruit is so powerful that his usage of it during his ten day battle with Akainu permanently changed the weather on one side of Punk Hazard, turning that side into a frozen wasteland.
Mihawk is the current holder of the title, “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.
Sengoku was the fleet admiral of the Marines pre-timeskip, succeeding Kong and preceding Akainu. He was also one of the major figures along with Whitebeard, Shiki, and Monkey D. Garp during the times when Gol D. Roger was still alive, and still continues to be in the present, even after his retirement from the Marines.
Even without his Devil Fruit powers, Sengoku has great strength and speed; he is also shown to have a strong will as he was able to resist Luffy’s unconscious burst of Haoshoku Haki.
Sengoku ate the Hito Hito no Mi, Model: Daibutsu, a rarer-than-Logia Mythical Zoan-class Devil Fruit which allows him to turn into a gigantic Daibutsu. This ability gives him a massive power boost to his already impressive strength, enough to cause the execution stand to collapse in one indirectly connecting punch, despite the combined effort of Luffy’s Gear Third and Mr. 3’s Candle Wall to absorb the attack. He can also launch an explosive shock wave with a palm thrust, enough to send a majority of the Blackbeard Pirates flying a fair distance.
Silvers Rayleigh, also known as the “Dark King”, is the former first mate of the Roger Pirates, known as the “Right Hand of the Pirate King”.
Rayleigh is extremely powerful, easily one of the strongest characters introduced.
He could intercept Kizaru’s attack when the Admiral was about to kill Roronoa Zoro without Kizaru noticing, and also managed to keep up with his light enhanced speed.
Rayleigh is one of very few people who can use all 3 types of Haki: Armament Haki, Observation Haki and Conqueror’s Haki.
Rayleigh infact has shown to possess great mastery of Haki, and made use of all three types while teaching Luffy about them, and training him in the basics.
2-MONKEY D. GARP
Monkey D. Garp is one of the most powerful Marines seen in the series so far. He’s a Marine vice admiral and also a “Hero” of the Marines, and as such is known for cornering and fighting Gol D. Roger many times. Roger also stated that he and Garp had almost killed each other on numerous occasions. As another true testament of sheer power, Garp defeated and nearly killed Don Chinjao in the past with a single punch, whose bounty was worth over 500,000,000 Berries in his prime and was said to be able to split a continent with a headbutt.
Garp got the distinction of “Hero of the Marines” from dealing with Rocks who were prominent 40 years ago, before the Pirate King Gol D. Roger came into power.
The extent of Garp’s power and fame is evident round the time of the Battle of Edd War, three years before the future Pirate King died. It was revealed that he was offered the promotion to the rank of Admiral more than once, but repeatedly refused the promotion.
Another example of Garp’s strength is when he was shown to easily strike down Marco of the Whitebeard Pirates and knock him back, despite having his Devil Fruit abilities activated at the time, which was something that both Kizaru and Akainu seemed unable to do.
1-MONKEY D. DRAGON
Monkey D. Dragon is the infamous leader of the Revolutionary Army who has been attempting to overthrow the World Government. He is the World Government’s greatest enemy and is the most dangerous and most wanted man in the world. Dragon is already a powerful threat in his own right, as well as having powerful subordinates such as Sabo, Ivankov, Bartholomew Kuma, and Inazuma who are in comparison, lower in rank. This only speaks volumes of Dragon’s true power.
When he was mentioned at the Summit War everyone froze, just at the thought of Dragon. Everyone is scared of him. He is at least Yonko level. Maybe the strongest character of the series.