The Void Century, also known as the Blank Period, is a 100-year time period in One Piece about which almost no records exist. Taking place about 900-800 years before the current storyline, it is believed that the 20 Kings united to fight against the Ancient Kingdom, which is completely untraceable now.
With the conclusion of the Void Century, the World Government was established. Consequently, the World Government has forbidden the study of this 100-year blank period. Even so, studying the Poneglyphs can reveal the true history, and some people have, surprisingly, already uncovered this history in One Piece. Here are the 10 people who know about the events of the Void Century.
The doctor of the Roger Pirates, Crocus was on Roger's ship a long time before the final journey to Raftel. During the Edd War, Crocus was seen as an active member of the Roger Pirates. After the journey to Raftel, in One Piece Chapter 959, when Roger became the Pirate King, once again, Crocus was seen aboard the Pro Jackson.
Since the Pirate crew found out the true history of the world, Crocus certainly did uncover all the truths about the Void Century as well. It seems that he also knows a bit about Roger's will, which is now inherited by Monkey D. Luffy.
Shanks hails from the West Blue and he sailed on the Oro Jackson as well. Being a member of the Roger Pirates, it is undeniable that Shanks sailed to Raftel with the rest of the crew. Since his Captain, Roger, uncovered all the secrets, it is likely that Shanks knows about them as well. Interestingly, Shanks has never been mentioned to be on the hunt for the One Piece.
Like Whitebeard, he seems to have chosen the path of a pirate for some other reasons entirely. Right from the very beginning of the series, Shanks has entrusted everything to Luffy.
Also known as The Clown, Buggy was also a part of the Roger Pirates once. Just like Red-Hair Shanks, he was an apprentice on the ship, although he didn't turn out to be as impressive as his friend. Since Buggy and Shanks were with Roger for the same amount of time, it makes sense that he went with the crew to Raftel as well.
Buggy seems to know a lot about history, however, he chooses to keep quiet about it for some reason of his own. Buggy may not be interested in the One Piece, or in fulfilling the Will of D, but he certainly is looking for other pieces of treasure that help him live out his days lavishly.
A former member of the Rocks Pirates and the Captain of the Whitebeard Pirates, Whitebeard was known as the man closest to One Piece when alive. However, as a Pirate, he was barely ever interested in the fabled treasure. For Whitebeard, finding a family took precedence over everything else, and as such, his care for the One Piece was negligent.
However, during one of his last meetings with Roger, the two talked about the Will of D and the Ancient Kingdom. Moments before his death, Whitebeard mentions the world turning upside down because of the revelation that finding the One Piece will bring, implying that he, indeed, knows about the Void Century and the D.
6 Scopper Gaban
Scopper Gaban was once the left-hand man of the Pirate King, Gol D. Roger. As one of his most trusted crew members, Gaban journeyed with the rest to Raftel as well. Undeniably, Gaban found out the history of the world, as did his Captain, Gol D. Roger. Surprisingly, after the Roger Pirates disbanded, Scopper Gaban is nowhere to be seen.
While Rayleigh has appeared a couple of times already, Gaban has barely ever been mentioned, which leads the fans to theorize that he might play an important role in the future of One Piece.
Also known as the Dark King, Silvers Rayleigh was the Right-Hand Man of Gol D. Roger and the First Mate of the Roger Pirates. Aside from being one of the strongest characters in the series, Rayleigh is also one of the most informative. As indicated by him at Sabaody Archipelago, he discovered the true history at Raftel. Rayleigh offered to confide to Nico Robin the events of the Void Century, however, she refused the proposal since she wanted to journey with the crew to find the history for herself.
Furthermore, the fact that Rayleigh knows the history is reflected in his bounty, which is still active decades after he retired as a Pirate.
4 Kozuki Oden
As befitting a man of his stature, Kozuki Oden is one of the few people who know the true history of the world. Being from the Kozuki Clan, the people responsible for the engraving of the Poneglyphs, Oden can read and write the ancient language. After joining Gol D. Roger's ship from Whitebeard's, Oden journeyed to Raftel and returned with the information of the Void Century.
Unfortunately, he isn't alive anymore, since he was brutally boiled alive in Oden soup by Kaido and the Shogun of Wano, Kurozumi Orochi.
3 Gol D. Roger
The Pirate King, Gol D. Roger is the only known person to have sailed their crew to Raftel. After finding out the true history of the Void Century and the secrets of the Government, Roger likely realized that he couldn't fulfill the Will of D. for some reason. Consequently, he turned himself in to usher a new age of Pirates moments before he died.
For now, Roger's legacy is carried by Luffy through the Straw Hat that's been passed on to him.
The Gorosei, also known as the Five Elder Stars, are the leaders of the World Government. In the entire Government hierarchy, including the Celestial Dragons, they hold the highest power. Since they're the uppermost power in the Government, they certainly know of the war that took place 900 years ago in the world of One Piece.
It has also been speculated that they're immortal, although there is no conclusive backing to that theory. Regardless, they've tried to bury the truth about the history time and again, implying that they're trying their to hide the atrocities they might have committed. During the destruction of Ohara, the Gorosei ordered the execution of Professor Clover since he 'knew too much'.
Contrary to popular belief, the Gorosei aren't the highest authority in the One Piece world. Imu-sama, a mysterious figure who sits atop the Empty Throne is even higher up the pecking order. Recently introduced during the Reverie arc, Imu was implied to have ordered a couple of cleansings in the past, primarily to keep every bit of information on the Will of D and the Void Century buried.
He also seems to be in possession of a giant Strawhat, although it is unknown to whom it belongs. Undoubtedly, Imu knows of the true history and is likely responsible for knitting it to some extent.