I'm not sure if you're being serious or not, but if you are, here you go:
As far as I know it started in 3e (though it seems to be a more codified version of the classifications in the 1e Deities and Demigods) with the 3e Deities and Demigods book. In Chapter 2 it defines Ranks of Divine Power as follows:
"Rank 0: Creatures of this rank are sometimes called quasideities or hero deities. Creatures that have a mortal and a deity as parents also fall into this category. These entities cannot grant spells, but are immortal and usually have one or more ability scores that are far above the norm for their species. They may have some worshipers. Ordinary mortals do not have a divine rank of 0. They lack a divine rank altogether.
Rank 1–5: These entities, called demigods, are the weakest of the deities. A demigod can grant spells and perform a few deeds that are beyond mortal limits, such as hearing a grasshopper from a mile away.
A demigod has anywhere from a few hundred to a few thousand devoted mortal worshipers and may receive veneration or respect from many more. A demigod controls a small godly realm (usually on an Outer Plane) and has minor control over a portfolio that includes one or more aspects of mortal existence. A demigod might be very accomplished in a single skill or a group of related skills, gain combat advantages in special circumstances, or be able to bring about minor changes in reality itself related to the portfolio. For example, a demigod of thieves might be able to change a stolen item so that it is no longer recognizable.
Rank 6–10: Called lesser deities, these entities grant spells and can perform more powerful deeds than demigods can, such as sensing certain phenomena from ten miles away.
Lesser deities have anywhere from a few thousand to tens of thousands of worshipers and control larger godly realms than demigods. They also have keener senses where their portfolios are concerned.
Rank 11–15: These entities are called intermediate deities. They have hundreds of thousands of mortal worshipers and control larger godly realms than demigods or lesser deities.
Rank 16–20: Called greater deities, these entities may have millions of mortal worshipers, and they command respect even among other deities. The most powerful of greater deities rule over other deities just as mortal sovereigns rule over commoners.
Rank 21+: These entities are beyond the ken of mortals and care nothing for worshipers. They do not grant spells, do not answer prayers, and do not respond to queries. If they are known at all, it is to a handful of scholars on the Material Plane. They are called overdeities. In some pantheistic systems, the consent of an overdeity is required to become a god."
Now 4e abandon the idea (though it did have gods, avatars and exarchs) and 5e brought back a simplified version with just quasi, lesser and greater deities. Both did away with the granularity of a number rank.
For my version of Divine Rank I am going to bring back the number rank, though it will be my own rating and will probably top out at 10. By bringing back divine rank I hope to create a simplified system that gives some/most epic monsters power beyond mortals without resorting to all of the gymnastics I did with the Epic Bonus, revised CR progression, +x to hit, etc. The current plan is to give epic creatures powers relative to their rank. Such as, a Rank 5 epic monster is resistant to the attacks of rank 3 or less monster and immune to attacks from Rank 0 or lesser creatures. Also, the hope is to be able divorce Divine Rank from CR so that you could have a lower CR Fey Lord that as a high Divine Rank.
The issue I've created is that the traits of a given rank effect the CR, making it a moving target. So, I am thinking about maybe my epic monsters have a CR relative to the Divine Rank. This could be overly complex though. Of course, this is not to different than the DMG which has CR adjustments qualified by the assumption of the level of the PCs that are expected to challenge it (dragon fear not effecting the CR for PCs over lvl 10 for example). Not sure of exactly what I am going to do, I am still working on it.