maybe its the Sol Kingdom or something, but that seems way too simple for that mindset.
So you know that book Kuma carries around? The figure on the front who looks a lot like Lady Liberty? It also resembles a Roman Figure known as Sol Invictus.
A minor deity (minor to the Planet gods) introduced to Rome named "Sol Indiges(Defied Sun)," who had a cult. This cult did things like modifying a statue of NERO (Nerona?) to Sol at one point.
As Rome expanded, and other cultures joined to become a melting pot. Sol Indiges started to absorb and be merged to other deities, including a huge EASTERN influence. This merged god became Sol Invictus(Unconquered/Invincible Sun).
An emperor of Rome who hailed from Syria named Elagabalus decided to try to make Sol from A GOD to THE GOD of Rome, and put the Planet Gods beneath him, making him God over all gods. For this he was assassinated. But the cult remained in society, and came back influential with Emperor Aurelian(Gold. Roger?) who brought Rome back together from its split of sub empires. His mother being a priestess of Sol.
Now let's see. Sun God with cult, mixed into other cultures (in OP a variety of kingdoms have their own sun emblem) but all symbolizing one Sun God. A Sun God who is then put above the Planet Gods, and the upper echelons assassinating those who place him above, and trying to wipe out his cults. Familiar?
Sol as a name is a very good guess.