The Four Emperors are the four most notorious and vastly powerful pirate captains in the world, but are neither allies nor enemies of one another, preferring to remain autonomous under most circumstances. These four individually reside within the second half of the Grand Line (known as the "New World"), exerting impressive influence and control over dozens of other pirate crews and self-governing islands.
In the decisive Battle of Marineford, Whitebeard, one of the Four Emperors, met his end towards the climax of the Paramount War. Blackbeard, his killer, subsequently usurped his position. Shanks, another member of the Four Emperors, arbitrated a ceasefire to end the aforementioned war.
Powers and AbilitiesEdit
As an entity, the Four Emperors are one of the Three Great Powers of the world, the others being the Seven Warlords of the Sea and Marines. Their strength and influence are such that they live quite literally as though they are emperors, doing mostly as they please. Individually, they are considered to be the most powerful pirates in the world, as well as having a powerful crew. Because of their power, they can declare chosen locations as their own; the mere declaration is often enough for others, both Marines and pirates alike, to acknowledge their authority.
In fact, in the New World, they each have a territory that they govern. These territories benefit from the protection the Emperors provide, keeping the borders safe from any faction that might want to invade them. It is only with the combined efforts of the Marines and the Seven Warlords of the Sea, as well as the distrust among them, that keeps their power in check. During the Battle of Marineford, the Marines and Warlords needed to fight together just to engage one of the Emperors, Whitebeard, and his crew. The arrival of a second Emperor, Shanks, immediately brought an end to hostilities, showing the power and influence they have without engaging in combat.
The Four Emperors themselves are not allied together as a coalition compared to the Seven Warlords of the Sea and follow their own individual paths. The possibility of two or more of the Emperors forming an alliance is enough of a threat to cause the World Government to panic, as seen when the World Government attempted unsuccessfully to prevent a meeting between Shanks and Whitebeard at one point. The World Government feared that the two Emperors may unite together and create a stronger threat. A war between two of the Emperors is considered a terrifying crisis, as Shanks' interception of Kaido's advancement on Whitebeard had taken the Marines by shock and awe, putting the World Government in a "cold sweat" as stated by one of the Marines.
They can motivate others to become pirates; Shanks inspired Luffy, and the death of Whitebeard inspired many pirates to travel to the Grand Line. On top of this, the influence these pirates have over others is far greater than any other noted group. With one declaration, the slave trade and pirate attacks on Fishman Island stopped after the island was declared to be under Whitebeard's control. Big Mom's tea parties indicate that her powers can reach even those of a sea quadrant far away from the New World or locations where strong people reside, and that her knowledge of the backgrounds of individuals who interest her can go far back.
After the timeskip Trafalgar Law cited that there are only two methods of surviving in the New World, and that is to be protected under the umbrella of an Emperor's dominion and become their ally or to constantly oppose their authority. At least Teach and Kaido are both gaining influence and strength in the form of amassing Devil Fruit powers, both in their own unorthodox methods.
Because of their immense power, it is necessary for factions aiming to oppose them to first strike an alliance with other factions in order to bring the Emperor down. However, even with multiple alliances amongst powerful pirates, the chances of defeating an Emperor are still extremely low.