Most know that Genshin Impact's Teyvat is currently governed by the Seven Archons, most likely being watched by Celestia. However, it's easy to forget or skip over some lore that talks about the original rulers of Teyvat, the Seven Sovereigns. These were dragon rulers that were there before the gods, before humans, and before the Primordial One came down and changed how things work. Genshin Impact players should have some knowledge of these ancient rulers before going into Natlan, a country said to have dragons intermingling with humans.
Being undermined by the Primordial One, the old Sovereigns cannot make use of their full power without their authority being rightfully returned to them. This has only been shown to happen with an Archon's death in the recent Fontaine Archon Quest, wherein Focalors killed her divinity and returned the power to Neuvillette. The Sovereigns are said to come from the Light Realm, a realm known for its ties to the elements -- so much so that it is also referred to as the elemental realm. These aren't the realms' only names, as it is also fittingly called the Vishap Realm.
Fontaine's release revealed more about the Old World than expected. From Neuvillette's character story alone, players learned that the original Dragon of Water had control over the Primordial Sea. It's said that all life comes from that sea, at least at first. Later on, when outside life developed with the interception of the Primordial One, the Primordial Sea was no longer the creator of all life.
When the Primordial One intercepted, they created the Human Realm as a mid-place between the Light Realm and the Void Realm. It's where life resides now and Genshin Impact's Vishaps and Sovereigns have lost a vast majority of their power. They no longer have the authority they used to since the Primordial One came down and weakened the Sovereigns and took said authority. However, the Sovereigns also weakened them in return.
Not all the Sovereigns are known or named, and not all dragons in-game are explicitly stated to have been a Sovereign. Currently, the only named and known Sovereigns are:
However, it's unclear if being the King of Dragons makes Nibelung a Sovereign or something else. Regardless, these are not the only known dragons of importance. Both Dvalin/Stormterror and Azhdaha are important, with Azhdaha being implied to be the Geo Sovereign through some of his titles such as Sealed King of Geo Dragons. Dvalin may not have be hinted as a Sovereign, but since he is one of Mondstadt's most important dragons (the other being Durin, one of Gold's creations) it isn't off the table.
Apep contains an entire world within himself, and that world is said to have birthed some ancient lifeforms. He attempted to absorb forbidden knowledge and fight against the Heavenly Principles but was corrupted in turn because of the effects of forbidden knowledge. Neuvillette is not the original Hydro Dragon, but rather a reincarnation. He had recently returned to his full authority through the death of Focalors. Nibelung was the Dragon King and has been dead since before the events of the game in a war with the Heavenly Principles.
As of the current version, no other Sovereigns are known of or confirmed. With Natlan as the upcoming nation, players should keep an eye out for more Sovereign lore in the event that the nation hides the old Pyro Dragon. There's even the possibility that other Sovereigns could be among them, since it's a nation where dragons and humans live together.