There are three titles for one supreme leader in the ancient Chinese culture:

(1)    What are you, the highest-in-command, resembling? 

  • Heavenly Monarch (天帝) — The supreme leader who represents the Heaven itself.
  • Heavenly Son (天子) — The Son of Heaven, implemented after the end of Earth Order, when Heaven comes into existence.

(2)    What era are you in?Edit

  • Heavenly Sovereign / Sui Sovereign (天皇 / 燧皇) — Granted to the highest-in-command, Heavenly Monarchs of the Fire Order Era.
  • Earthly Sovereign (地皇) — Granted to the highest-in-command, Heavenly Monarchs of the Earth Order Era.
  • Human Sovereign (人皇) — Granted to the highest-in-command of the human race in the current era where Heavenly Monarch was taken down by Heaven and Heavenly Son is now implemented to the highest-in-command.

(3)    What defines you specifically from the other sovereigns?Edit

  • Great Sui
  • Nong Sovereign (aka. God of Agriculture) 
  • Tai Sovereign 

Eg.     The creator and first leader of Fire Order Era (Heavenly/Sui Sovereign), and also the highest-in-command (Heavenly Monarch), the world have given him his personal, unique title of Great Sui. 
 — Heavenly / Sui Sovereign, Heavenly Monarch, Great Sui. 

Note: When Sui Sovereign undirected specefically to anyone else, it is commonly referred to the first Sui Sovereign, Great Sui.Edit