The Void Century is a 100-year gap in history that contains many important incidents. After learning about the events that took place during the Void Century, a person is said to discover the true history of the world. For this reason, the World Government strictly forbade anyone from reading the Poneglyphs, as they were inscribed with the correct information.
But not every person was willing to play by their rules. Many One Piece characters took the risk and began deciphering the writings on the Poneglyphs. They uncovered the darkest secret of the World Government, which made them notorious criminals. Aside from these criminals, there are other One Piece characters who know about the Void Century.
8 Imu
Imu is the leader of the World Government. Imu passes orders to the Five Elders, which they carry out without fail. The existence of Imu is a great secret that has been protected by the World Government for ages. The organization has maintained the charade of the Empty Throne being unoccupied.
Imu's age remains unknown, but it is plausible to assume that they existed before the formation of the World Government. They know about Nefertari Lily, and they were probably responsible for her death as well. Imu is knowledgeable about the Void Century and knows about every event that took place during that time.
7 Kozuki Oden
Kozuki Oden was a legendary samurai from Wano. He was reckless, powerful, and, above all, free-spirited. Oden's desire was to sail the seas and explore different islands. His dream came true when the Whitebeard Pirates crashed onto the shores of Wano. Oden traveled with the crew until Roger requested that the samurai accompany him on his final journey.
Oden had many fabulous adventures with the Roger Pirates, and with his ability to read the Poneglyphs, the Roger Pirates found Laugh Tale. Needless to say, they wouldn't have learned the true history of the world without Oden.
6 Gol D. Roger
Gol D. Roger was the biggest enemy of the World Government at one point. He managed to do the unthinkable when he found Laugh Tale and the One Piece. Roger also learned about the Void Century, and it probably influenced his decision to not take the treasure.
Following the success of his voyage, Roger disbanded the crew and turned himself in to the Marines. It is highly likely that Roger wanted to do something so that the right person would find the One Piece. Before his execution, Roger told the entire world that he had left his treasure on a certain island, thus starting the Great Era of Piracy.
5 Five Elders
To most of the world, the Five Elders are the highest authority within the World Government, as Imu's identity is kept hidden. The Five Elders have overseen some of the most nefarious missions that were beneficial for the World Government.
Much about them remains a mystery, but one thing is for sure: they are aware of the Void Century and what exactly transpired during those 100 years. The Five Elders are overly protective of this secret and will try anything in their power to erase any witnesses. All five of them seem quite powerful, and it won't be long before their powers are also revealed to the audience.
4 Silvers Rayleigh
Silvers Rayleigh is considered one of the most dangerous pirates in the world, mainly because of his affiliation with the Roger Pirates. Even after hanging up his boots, Rayleigh is still hunted by the World Government.
Rayleigh confirmed that he knew about the true history of the world during the Sabaody Archipelago arc. However, he did not divulge any important information that would have potentially ruined the adventure of the Straw Hats.
3 Whitebeard
Whitebeard formed his own crew after leaving the Rocks Pirates. He gained a great deal of notoriety because of his incredible strength. He was eventually given the title of "Strongest Man in the World." Whitebeard was Roger's greatest rival, and they fought each other many times. But they respected each other a lot. Roger met Whitebeard before his execution and told him about the Will of D and the other secrets of the world.
Whitebeard decided against sailing to Laugh Tale because he did not care about treasures. He just wanted a family, which he found in his crewmates.
2 Clover
Clover was the leader of the scholars of Ohara. He and the rest of the scholars secretly studied the Poneglyphs in an attempt to discover the truth about the Void Century. After a long and strenuous effort, they managed to uncover the secret.
Unfortunately, the World Government came to know about the scholars and their crimes. The organization wasted no time in sending its forces to Ohara to gather all the scholars. Clover requested to talk to the Five Elders before his impending death. In the brief conversation, Clover implied the existence of the Great Kingdom and the misdeeds of the World Government. Sadly, the Five Elders gave Spandine the order to shoot before he could finish.
1 Jaguar D. Saul
Jaguar D. Saul was presumed dead after he was frozen by Aokiji in Ohara. Luckily, the Vice Admiral managed to survive, although he did pick up some injuries. Dr. Vegapunk confirmed that Saul had survived the Buster Call. The scientist stated that he met Saul, who was covered in bandages, probably to hide the burn marks on his body.
Saul had a bunch of other giants dig up the books that belonged to the scholars of Ohara. The giants took the manuscripts back to Elbaf for safekeeping. It is plausible to assume that Saul went through the books and found out about the horrific secrets of the World Government, including the Void Century.