Shogun

The shogun is the official title for the monarchic ruler of the Wano Country.

Overview
The shogun is the supreme ruler of the Wano Country and all that reside within it. Below them are the daimyo, who rule over the different regions of Wano.

The title of shogun can be inherited from parent to child. However, if the heir proves to be unworthy of the status in some way, then the parent can disavow them of their birthright. If the shogun has no legitimate heirs to pass the title to by the time they pass on, then one of the daimyos will become the new shogun.

Shoguns

 * Kozuki Sukiyaki was the shogun long ago and ruled it with great responsibility and compassion. He was presumably killed by the Kurozumi Family in their plot to take the country for themselves. However, he was actually imprisoned by them. By the time he escaped, his son Kozuki Oden had already been killed and Wano was drastically changed by Orochi and the Beasts Pirates. Out of shame, he disguised himself as the tengu hermit Tenguyama Hitetsu and let everyone believe that he was dead. He revealed his true identity only to Nico Robin after his grandson Momonosuke took over as shogun, but he intends to continue keeping his survival a secret from everyone else.
 * Kurozumi Orochi was the shogun from the disgraced Kurozumi Family. After disposing of Sukiyaki and earning the support of Kaidou and his crew, he was able to take control of the country and use his authority to make its people suffer for the indignity he was forced to endure while young. However, he was then betrayed by Kaidou, who sought to make his son Yamato the new shogun even though Yamato doesn't want to, and was later killed by Denjiro, thus ending his reign for good.
 * Kozuki Momonosuke is the current shogun of Wano, following the Ninja-Pirate-Mink-Samurai Alliance's defeat of Kaidou and Orochi during the Fire Festival. He promised to free the country's citizens from tyranny and slavery and to return the land to a paradise. He also announced that the toxic factories will be demolished.

Trivia

 * In real-life Feudal Japan, the shogun was the commander-in-chief while the country was ruled by the emperor. However, the emperor was actually a mere figurehead who possessed little to no actual power while the shogun was the de facto ruler of Japan.
 * Ironically though, the reverse can be said with Shogun Orochi being the figurehead while the Emperor Kaidou was the true ruler of Wano.