The Four Emperors have always stood on top of the pirate food chain in One Piece. They are regarded as the strongest pirates whom even the Marines cannot approach without careful planning. Each of them possesses might and influence that can rival any kingdom -- but even so, their ranks have experienced a few changes throughout the series' long tenure.
When Luffy first set sail, the title of the Four Emperors was held by Shanks, Whitebeard, Big Mom and Kaido. Whitebeard's death during the war at Marineford prompted a change to the lineup. Blackbeard, who stole his former captain's Devil Fruit powers, took the late Emperor's title, while Luffy's consecutive feats after entering the New World resulted in him being regarded as the Fifth Emperor. With Big Mom and Kaido's recent defeat in Wano, One Piece has finally introduced its new Four Emperors.
With Law and Kid successfully defeating Big Mom and Luffy burying Kaido, Wano was finally freed from the dictatorship of the Animal Kingdom Pirates. Luffy and co. earned themselves some downtime and partied with the samurai in celebration of their victory. Meanwhile, new bounties came out for the three pirate captains who fought against the Big Mom-Animal Kingdom Pirate alliance. The bigger shock, however, came when the new Four Emperors were announced. With Big Mom and Kaido removed from the list, an unexpected character filled the missing spot: Buggy The Genius Jester.
Buggy has always been popular as meme material, often regarded as one of the strongest characters in the series as a joke. He is one of the many comic reliefs in One Piece, but his rise in rank is not necessarily unfounded. Though he may be lacking in strength, he makes up for it with cunning intellect and a keen sense for survival. His luck and survival skills have allowed him to get out of major historical events alive -- including the grand Impel Down prison break and Marineford war -- enabling his candidature to be part of the Seven Warlords of the Sea.
One Piece fans found Buggy's unexpected status as a Warlord funny; however, the gag may have overstayed its welcome as him being one of the Four Emperors has elicited a mixed reaction. Being an emperor requires unparalleled strength and influence, and it is rather questionable whether Buggy possesses the qualifications to even be considered as one. This raises the question of how he managed to gain his new and best title yet.
Aside from successfully surviving the events at Impel Down and Marineford, Buggy's extensive background also helped bolster his status. After all, he is a former member of Roger Pirates along with none other than Red-Haired Shanks, who also acknowledged his existence when they met in Marineford. After becoming a Warlord, Buggy started to run a mercenary group and expanded his influence by selling his services to those willing to pay -- and his henchmen were no simple pushovers. In fact, Hajrudin, who is now a captain in Luffy's Grand Fleet, was a former employee of Buggy's business.
Although the extent of Buggy's influence is yet to be revealed, it's fairly safe to assume he had enough might under his command to resist the Marines' attempt to arrest him when the Seven Warlord system was abolished. Given his luck, it won't be surprising if Buggy has managed to recruit more powerful warriors -- say Edward Weevil -- to join his crew. The question now is what Buggy's role will be in One Piece's upcoming final arc.