OnePiece is one of the longest-running manga series of all time. One of the main reasons behind its success is the diverse cast of the series. There are hundreds of characters in One Piece and every single one of them is unique in their own way.
However, there is a major drawback of having so many characters, which is being unable to give each of them proper attention. There are many powerful characters that the fans are yet to see in action, and there are a lot of mysteries surrounding them. It is going to be a long time before any of them are seen in action.
10 Dracule Mihawk
Known as the Strongest Swordsman in the World, Dracule Mihawk oozes brilliance. He was the first Shichibukai to be revealed in the series. Mihawk has no crew and he prefers to live alone on a secluded island. Mihawk possesses the all-black blade, known as Yoru, which is one of the 12 Saijo O-Wazamono swords.
So far, Mihawk has not been engaged in a proper fight. He was involved in the Summit War but faced no real challenge, and he was among the few characters who remained unscathed throughout the war.
9 Monkey D. Dragon
Monkey D. Dragon is the leader of the Revolutionary Army, which makes him the biggest threat to the authority of the World Government. It is unknown how Dragon started the Revolutionary Army or how he gained so much power.
Dragon's powers still remain a mystery and there is no information about his devil fruit or Haki. Regardless of his abilities, it is quite obvious that the leader of the Revolutionary Army won't be a weakling. It is very likely that he will be seen in action in the next arc.
8 Shanks
One of the Yonko, Shanks is among the strongest characters in OnePiece. With the help of his strength and his crewmates, Shanks managed to reach the status of a Yonko. He is able to use all three types of Haki, and in particular, his Conqueror's Haki is very powerful.
With his Conqueror's Haki, Shanks was able to damage Whitebeard's ship. He is also among the few known people who are capable of damaging Kaido. The next arc of OnePiece will very likely feature Shanks as one of the most important characters.
7 Blackbeard
Blackbeard is considered a huge threat by the World Government. In the Reverie arc, Imu had his poster along with a handful of others. Blackbeard's real strength is still unknown. He possesses two very overpowered devil fruits, which make him very dangerous.
The Gura Gura no Mi alone is enough to decimate an entire island. Blackbeard hasn't shown his true power yet, but that will change in the future.
6 Boa Hancock
Boa Hancock rules over Amazon Lily, and she is also the captain of the Kuja Pirates. Boa's strength is outrageous. She is armed with the Mero Mero no Mi, which is a paramecia-type devil fruit. The devil fruit allows Boa to turn anything that she touches into stone.
It is difficult to counter her devil fruit and to make matters worse, Boa Hancock possesses all three types of Haki. Her involvement so far in the series has been limited, but with the Shichibukai system gone, she will be involved in more battles.
5 Edward Weevil
He is the self-proclaimed son of the great pirate, Edward Newgate. Led by his mother, Weevil has been actively chasing the remnants of the Whitebeard Pirates in order to get his hands on the fortune left behind by his late "father."
Weevil has a bounty of 480,000,000 beris, and his strength has been compared to that of young Whitebeard by Admiral Kizaru.
4 Ryokugyu
Ryokugyu is one of the two new Admirals who joined the Marines during the two-year time-skip. He made a brief appearance during the Reverie arc, where fans caught the silhouette of the Admiral. According to Ryokugyu, he has not consumed any food in the last three years, yet he managed to reach the status of an Admiral. So far there is no information available on Ryokugyu's devil fruit or his other abilities.
3 Scopper Gaban
A member of the infamous Roger Pirates, Scopper Gaban was one of their strongest fighters. In the anime, during the crew's clash versus the Whitebeard Pirates, Scopper Gaban fought against Kozuki Oden, who was a master at using Busoshoku Haki. However, the battle was off-screen and the fans didn't get a chance to see his power. Being one of Roger's closest friends, it is plausible to assume that Scopper Gaban possesses insane strength.
2 Vegapunk
Vegapunk is without a doubt the smartest character in the series. He has been forced to work with the World Government and he has created many inventions for them. He managed to create a devil fruit using Kaido's lineage factor, which was later eaten by Kozuki Momonosuke. Vegapunk is yet to make a proper appearance in the series.
1 Kizaru
Kizaru made his debut in OnePiece during the Sabaody Archipelago arc, where he fought against several members of the Worst Generation. He is one of the strongest Marines in the series. Kizaru showed off his strength and he was easily able to overwhelm them.
He was also able to fight against Rayleigh, but the fight lasted for only a few seconds. So far, Kizaru has never gone all-out in a fight. He has only shown glimpses of his power, and one would hope that it changes after the Wano arc.