The One Piece world is currently in the Great Pirate Era which was started by the Pirate King, Gol D. Roger, moments before his death. Once he announced the existence of the One Piece, millions took to the seas in order to find his treasure.
Before this age, the seas were not as turbulent, however, there were still those who followed their dreams and took to the sea. Several legends of the old days have already appeared in the story, however, there are some who are yet to make their appearance and the fans are eagerly waiting for.
7 Captain John
Captain John is one of the former members of the Rocks Pirates. Interestingly, Captain John made an appearance as a zombie during the Thriller Bark arc of One Piece. Moria, one of the former Warlords, had acquired his body somehow and with Hogback's help, he was able to animate it.
Sadly, this Captain John was far from his prime strength. While his strength was certainly known to be legendary, as a zombie, he was weak. The real Captain John has never appeared in the series. It is possible that fans will see him in the God Valley flashback in the future.
6 Wang Zhi
Wang Zhi is yet another powerful pirate who is a remnant of the Rocks Pirates. Just like Captain John, he was introduced during chapter 957 when Sengoku talked about Rocks and his formidable pirate grew.
Wang Zhi is yet to make an appearance. Unlike Captain John, he was not present on Thriller Bark. What fans do know, however, is that he is potentially alive, even now. Until the two-year timescape, Wang Zhi ruled over Fullaled Island. During the Rocky Port Incident, he was confronted by Blackbeard and ousted from his seat. Currently, his whereabouts are unknown. Fans have not yet seen his face but in the future, it is possible that he will appear in the story or, perhaps, fans will see him in a flashback concerning either The God Valley incident or the Rocky Port Incident.
5 Shiki
Shiki is yet another legendary figure in the One Piece world. He is known to have been one of the major forces during the era of Gol D. Roger. He appeared as the main antagonist in One Piece: Strong World. However, he is yet to make an appearance in the main story.
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Shiki is known to have escaped from Impel Down after Roger's execution. His current whereabouts remain unknown. Shiki's silhouette appeared in One Piece 957 when Sengoku talked about the remnants of the Rocks Pirates. He was also one of the many famous pirates under Rocks' flag. Whether or not he will appear in the story at some point in the future remains to be seen.
4 Silver Axe
Silver Axe is yet another legendary figure who ruled the seas along with the Rocks Pirates before the age of Gol D. Roger. Very little is known about him and his life as a pirate, however, Sengoku hailed him as a legendary pirate of the old times.
After the God Valley incident, his whereabouts remain unknown. It is possible that he will make an appearance later on in the series. However, so far, Silver Axe is yet to appear.
3 Rocks D. Xebec
Rocks D. Xebec is quite possibly one of the biggest legends in the One Piece world. It is believed that he led the most powerful crew of all time before the age of Gol D. Roger began. The Rocks Pirates were a pretty powerful bunch who terrorized the seas and acted like a terrorist organization. Even the World Government could not stop them alone.
Rocks himself wanted to be King of the World. He met his end at God Valley, 38 years ago, when the Roger Pirates teamed up with the Marines to defeat the Rocks Pirates. He's known to have died in the encounter, however, whether that is true or not remains to be seen. Rocks has not yet made an appearance in the story.
2 Vegapunk
Vegapunk is a living legend in the One Piece world. He was born in the South Blue in the kingdom of Baldimore. Vegapunk is known to have incredible scientific genius and his brain is known to be 500 years ahead of humanity. Currently, he works with the Navy and aids them in their research. Vegapunk is yet to make his true appearance in One Piece, however, his character has been relevant from before the timeskip. Inevitably, he will end up making a true appearance in the Egghead Island arc of the series. So far, three of his six bodies have been revealed to the fans but the Stella, also known as the main body, has not appeared just yet.
1 Joy Boy
Joy boy is a major character who was active during the Void Century of the One Piece world. It is believed that he fought the World Government and led the war against the 20 Kings when the Ancient Kingdom clashed against them. Joy boy is known to have made a promise to the Mermaid Princess to take the Fishman and Merfolk to the surface.
As fans know, he failed in keeping this promise and is likely to have died in the war. Joy boy held the same Devil Fruit that Luffy currently possesses and he is also the same person who was worshiped by many as Nika, the Sun God. He has not yet appeared in One Piece, however, in the future, he is sure to be a massively important character.