One Piece consists of some of the strongest characters that we've seen in anime and much of it is down to Eiichiro Oda's consistent portrayal of the strength of the characters. These characters comprise of some very powerful pirates and even some of the marines who chase them across the oceans.
While the current list of the strongest characters will include big-shots like Blackbeard, we're going to be looking over the strongest known characters in One Piece, pre-timeskip. This list will include characters who we have seen fight to some extent, and thus, will be feat-based for the most part. Let's get started then, shall we?
Note: Characters, such as Dragon, who have not shown their powers at all are not included in this list.
10 Boa Hancock
Boa Hancock is also known as the Snake Princess and she's the ruler of the Amazon Lily island. Before the time-skip, Boa Hancock was just as strong as she is right now. She was already established as a user of all three Haki types. Before the war of Marineford, Sengoku praised her fighting prowess quite highly.
With a powerful Devil Fruit in Mero Mero no Mi and strong Armament Haki that was easily able to keep Smoker at bay, it is easy to see why Boa Hancock is on this list. She may find it difficult to creep into the post-time-skip Top 10, however.
9 Aokiji
Aokiji served as a Navy Admiral before the time-skip in One Piece and was actually the first Admiral to reveal his powers. Making his first appearance at Long Ring Long Island, Aokiji displayed his abilities by taking out nearly all of the Straw Hat Pirates on his own.
During the war of Marineford, he was pitted against Diamond Jozu, and he did fairly well. Aokiji defeated Jozu, however, that was largely due to the fact that Jozu was distracted due to Whitebeard's health condition during the fight.
8 Kizaru
One of the Three Admirals of the Navy, Kizaru made his first appearance during the Sabaody Archipelago arc where he single-handedly defeated four Supernovas without even trying. That was expected of him, however. During the war of Marineford, Kizaru fought against Marco of the Whitebeard Pirates and proved to be equal to him, at the very least.
Unfortunately, Kizaru didn't feature much in the war and his small skirmishes against Marco and Whitebeard isn't something to properly scale him off of. Nonetheless, he is easily strong enough to make the top 10.
7 Marco
The right-hand man of the strongest person in the world, Marco was easily among the strongest in One Piece, pre-timeskip. He was strong enough to fight and overpower Kizaru, inflict injuries upon Aokiji, and even go toe-to-toe against Akainu at Marineford.
Just like Jozu, Marco was incapacitated during the war due to Whitebeard's health. However, what's surprising is the fact that he was able to fight despite being shot several times by Kizaru and being cuffed with seastone. After the war, the Gorosei believed Marco to be one of the four people strong enough to defeat Blackbeard, implying he was incredibly powerful even back then.
6 Mihawk
The 'Strongest Swordsman in the World', Dracule Mihawk also ranks among the 10 strongest characters. Mihawk was was already at the pinnacle of his powers pre-timeskip, and that showed during his fight against Zoro, where the latter was easily outclassed.
Furthermore, Mihawk also tried to fight Whitebeard at Marineford but was stalemated by Diamond Jozu instead. He is certainly strong, but definitely not enough to break into the top 5, which we're certain that some may disagree with.
5 Silvers Rayleigh
Rayleigh made his debut during the Sabaody Archipelago arc of One Piece as 'the ship-coating man'. Later, it was revealed that Rayleigh was the Right-Hand Man of Gol D. Roger and was renowned as the 'Dark King'. Despite his old age, Rayleigh was strong enough to fight against Kizaru on equal footing and inflicting injuries on him.
According to Kizaru, a whole fleet of Navy would be needed to capture Rayleigh, while Garp stated that the Navy wasn't strong enough to capture him while focusing on Whitebeard, despite Kizaru being busy with him already. This is further backed up by the fact that Rayleigh was an adept user of all 3 Haki types and a master swordsman even back then. It goes without saying that he was incredibly powerful prior to the two-year time-skip.
4 Akainu
Another one of the Navy Admirals, Akainu was easily the strongest of the all even before the time-skip. With the powers of the Magu Magu no Mi, he was strong enough to fight against the likes of Whitebeard to some extent. Even though Whitebeard was sick and dying, fighting a monster as strong as he is required one to have a lot of courage and power.
He was one of the few characters to inflict injuries on Whitebeard, and he even clashed against strong characters like Marco, Vista, Ace, among others. Akainu then went on to become the Fleet Admiral of the Navy.
3 Sengoku
Also known as the Buddha, Sengoku as also among the strongest characters in the series before the two-year time-skip, and rightfully so. Being the Fleet Admiral of the Navy, Sengoku was one of the strongest in their ranks at the time, if not the strongest.
With the powers of the Hito Hito no Mi, Model: Daibutsu, Sengoku saw to it that those who stood in his way were crushed. During the Paramount War, he was powerful enough to fight against the entire Blackbeard crew on his own, showcasing his superior strength to the fans.
2 Monkey D. Garp
One of the strongest characters in One Piece even now, Garp easily ranks among the strongest characters before the time-skip. Although he showed little of his abilities back then, it is known that he combined with Sengoku to defeat Shiki, a famous pirate.
Garp was also known to have fought against Roger on countless occasions back then. He was also named the Hero of the Marines, which implies that he was certainly the strongest among their ranks.
1 The Yonko
The Yonko are the four strongest pirates in the world of One Piece, as explained by Garp during the post-Water 7 arc. Before the time-skip, their ranks were made up of Big Mom, Kaido, Shanks, and Whitebeard. All four of them were on the same level, more or less. However, it is a known fact that Whitebeard was the strongest among all of them; something that even Shanks acknowledged.
At some point during the two years, Blackbeard joined their ranks after the death of Edward Newgate at Marineford. Their menace is truly unmatched and even the strongest characters don't dare to get close to them.