When it comes coining names, you can use any name you like but it is usually capitalized, e.g. the Saviour, the Son of God, the Messiah, the Enlightened One.

Student or Learner
Is the phrase "the great one" correct in English? By "the great one (of the planet)", I intend it to mean "(if the planet has one real king to rule all other people, then it is called "the great one (of the planet)". I am not sure if it is natural in English.
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Here's a scenario set in ancient China when a numerous small kingdoms are vying for the holy
grail of controlling the great land in frequent economic and millitary conflicts.
Now there is a king who starts to show his great power in subduing other lords and is about
to unite the different kingdoms into one until he meets his nemesis, whose wisdom to understand the world, determination to conquer enemies, and strength to secure victories are all too impressive and often put the king in hard times.
That night the king kneels in his garden and looks into the skies, shouting "Am I not the great one on the earth, my Lord? You are the Great One of the Heaven and has sent me to the earth to unite the people on the earth to worship you. Why do you now send another man to compete with me?"
Source: My English writing practice
When it comes coining names, you can use any name you like but it is usually capitalized, e.g. the Saviour, the Son of God, the Messiah, the Enlightened One.
I am not a teacher or a native speaker.
You appear to be completely unaware that "great one" is a set phrase:
Now the king is a great one for politics. But whether "the great one" or "The Great One" can be used that way in the context of the OP is not clear. It seems to be both Yes and No. Hence the thread.Definition of great one: one especially enthusiastic or clearly of a particular habit of mind or action —used with for
a great one for skiing
a great one for the ladies
— Jack Iams
Source: Merriam-Webster Dictionary
https://www.merriam-webster.com/dictionary/great%20one
In the Lord of the Rings, Saruman was honored as, before he became a traitor, "The Skilled One", who won great respects from Gandolf, the wisest of the Maiar.
So the question of this thread remains. Is the answer a Yes?
Retired magazine editor and native British English speaker - not a teacher