I truly enjoyed the recent, excellent review of the new Mythic Odysseys of Theros that can be found here. One particular quote stood out to me:
In Forgotten Realms, 5th Edition D&D's default setting, gods exist – they power clerics and paladins – but they've taken a step back. They aren't directly acting in the realms, or even indirectly for the most part. Theros is very different. The gods are involved in the world. They squabble with each other, using people and monsters as pawns. More importantly, the gods need followers. In Theros, belief and dreams can become real over time. The people of Theros have dreamed the gods into existence and their belief keeps them alive. They don't realize that – but the gods do and often resent it. That drives some of their behavior, quests, and schemes. So in Theros, more than any other plane, devotion from mortals provides the gods with their divine power.
This reminded me of the classic play in D&D, and more specifically, the delineation between Demigods, Lesser Gods, and Greater Gods.
A. OD&D.
When OD&D first came out, the Cleric was introduced as one of the three original classes (Fighting Man, Magic User, Cleric ... although in keeping with the naming convention, perhaps Deity Person would have been more appropriate?). Notably, they were presented primarily as being just a cross between the other two classes, with the introduction for them stating, "Clerics gain some of the advantages from both of the other two classes (Fighting-Men and Magic-Users) ...." The reminder of the supplement does not mention gods or deities.
Bonus Fun Fact: While AD&D went on to have the notorious elf/spirit/resurrection restriction, OD&D allows humans, dwarves and elves to be raised .... but not halflings.
The last OD&D supplement was Gods, Demi-Gods, & Heroes, by Robert Juntz and James Ward. Enjoyably, the introduction (by Tim Kask) stated "This volume is something else, also: our last attempt to reach the “Monty Hall” DM’s. Perhaps now some of the ‘giveaway’ campaigns will look as foolish as they truly are. This is our last attempt to delineate the absurdity of 40+ level characters." Luckily, this volume completely ended the Monty Ha(u)l campaign! ahem
While the supplement contained different mythologies that we would later see in Deities & Demigods, it did not divide the various deities, monsters and heroes into types; in addition, it rarely touches on the issue of worship. References to campaign clerics, or adventurers, "worshipping" or observing deities contained in this book are, at best, scattershot. For example, it is written that Bes might bestow a luck stone for great gambles, but without referring to clerics, worship, and it specifically states that it is with "no strings attached." The only reference to clerics, priests, or woshippers in the entire book are a few references under a few gods; Osiris (few priests, can be granted a wish), Kali (demands human sacrifice), Hephaestus (few worshippers, might get magic shield), Uller (worshippers get a permanent bonus to movement!!!!). Essentially, despite the warning at the front, the supplement functions more as an Monty Haul Monster Manual than as something useful for DMs. "If you stat something, it can die."
The general attitude regarding deities (this being the last supplement) is reflected in the general tenor of OD&D; character sheets of the time rarely, if ever, mentioned the deity of a character.
B. AD&D
The emphasis changed with AD&D. Suddenly, religion (in the D&D world) mattered. The famous "orange" character sheets from 1981 had an explicit space for religion and patron deity at the top of the character sheet- with the same prominence as class, level, alignment, and race.
Aside: Character sheets should still have wills.
The Player's Handbook explicitly discusses that the cleric is devoted to a deity (or deities), and can build a religious stronghold dedicated to the deity (or deities). It also states that the cleric must be the same alignment as the deity the cleric serves.
Notably, the 1e PHB ties in the spells that the Cleric receives to the worship of the deity. On page 40, it states that while 1st - 4th level spells are granted by the lesser servants of the cleric's deity, 5th level spells and higher are granted by the deity itself. It goes so far as to state that the cleric must supplicate the deity for the granting of these high level spells and can be judged accordingly.
This became more explicit with the publication of Deities & Demigods, by James Ward, in 1980. There is a fun little history here:
www.enworld.org
In the book, the delineation of spells become more clear; clerics gain 1st and 2nd level spells on their own (knowledge and faith). Then it changes up a little, depending on the "ranking" of the god. All other spells are gained through prayer.
Demigods: Grant 3rd-5th level spells directly, and the cleric cannot get higher level spells.
Lesser Gods: Grant 3rd-5th level spells through minions, grants 6th level spells directly, and cannot grant 7th level spells.
Great Gods: Grant 3rd-5th level spells through minions, and 6th and 7th level spells directly.
Suddenly, the hierarchy matters a great deal! But wait, what is this hierarchy? What does it mean?
C. I AM THE LIZARD KING! I CAN DO ANYTHING!
I am eliding the remainder to the cleric/deity section to get back to the original reason that I decided to make this quick dive into history; the review of Theros. If you wait long enough, everything comes around again. Which is why you will take my flannel shirts out of my cold, dead hands.
Anyway, the very last section of Deities & Demigods before the listing of pantheons is titled DIVINE ASCENSION. Who doesn't like the sound of that? In a nutshell, it details how a PC can be raised up to become a demi-god! And how does that happen? Well, one of the conditions is that the PC must accumulate a body of sincere worshipers. Moreover, it was already stated that "The source of a deity's godheads is in some way connected to his or her earthly worshipers, though in what manner the gods derive this power is a mystery totally beyond mortal (or immortal) comprehension. However, it is true that a god's power often increases or decreases as the number of his worshipers varies. Thus deities, and clerics as their agents, constantly try to increase the quantity and quality of their worshipers."
The combination of factors leads to the ineluctable conclusion, oft-seen in AD&D, that in a polytheistic campaign, you would have deities battling it out via proxies for worshipers, as worshipers (both in number and power) had some bearing on the deity's power, which is turn also had some bearing on the power of those that worshiped (in terms of both temporal power and the ability to cast spells).
In Forgotten Realms, 5th Edition D&D's default setting, gods exist – they power clerics and paladins – but they've taken a step back. They aren't directly acting in the realms, or even indirectly for the most part. Theros is very different. The gods are involved in the world. They squabble with each other, using people and monsters as pawns. More importantly, the gods need followers. In Theros, belief and dreams can become real over time. The people of Theros have dreamed the gods into existence and their belief keeps them alive. They don't realize that – but the gods do and often resent it. That drives some of their behavior, quests, and schemes. So in Theros, more than any other plane, devotion from mortals provides the gods with their divine power.
This reminded me of the classic play in D&D, and more specifically, the delineation between Demigods, Lesser Gods, and Greater Gods.
A. OD&D.
When OD&D first came out, the Cleric was introduced as one of the three original classes (Fighting Man, Magic User, Cleric ... although in keeping with the naming convention, perhaps Deity Person would have been more appropriate?). Notably, they were presented primarily as being just a cross between the other two classes, with the introduction for them stating, "Clerics gain some of the advantages from both of the other two classes (Fighting-Men and Magic-Users) ...." The reminder of the supplement does not mention gods or deities.
Bonus Fun Fact: While AD&D went on to have the notorious elf/spirit/resurrection restriction, OD&D allows humans, dwarves and elves to be raised .... but not halflings.
The last OD&D supplement was Gods, Demi-Gods, & Heroes, by Robert Juntz and James Ward. Enjoyably, the introduction (by Tim Kask) stated "This volume is something else, also: our last attempt to reach the “Monty Hall” DM’s. Perhaps now some of the ‘giveaway’ campaigns will look as foolish as they truly are. This is our last attempt to delineate the absurdity of 40+ level characters." Luckily, this volume completely ended the Monty Ha(u)l campaign! ahem
While the supplement contained different mythologies that we would later see in Deities & Demigods, it did not divide the various deities, monsters and heroes into types; in addition, it rarely touches on the issue of worship. References to campaign clerics, or adventurers, "worshipping" or observing deities contained in this book are, at best, scattershot. For example, it is written that Bes might bestow a luck stone for great gambles, but without referring to clerics, worship, and it specifically states that it is with "no strings attached." The only reference to clerics, priests, or woshippers in the entire book are a few references under a few gods; Osiris (few priests, can be granted a wish), Kali (demands human sacrifice), Hephaestus (few worshippers, might get magic shield), Uller (worshippers get a permanent bonus to movement!!!!). Essentially, despite the warning at the front, the supplement functions more as an Monty Haul Monster Manual than as something useful for DMs. "If you stat something, it can die."
The general attitude regarding deities (this being the last supplement) is reflected in the general tenor of OD&D; character sheets of the time rarely, if ever, mentioned the deity of a character.
B. AD&D
The emphasis changed with AD&D. Suddenly, religion (in the D&D world) mattered. The famous "orange" character sheets from 1981 had an explicit space for religion and patron deity at the top of the character sheet- with the same prominence as class, level, alignment, and race.
Aside: Character sheets should still have wills.
The Player's Handbook explicitly discusses that the cleric is devoted to a deity (or deities), and can build a religious stronghold dedicated to the deity (or deities). It also states that the cleric must be the same alignment as the deity the cleric serves.
Notably, the 1e PHB ties in the spells that the Cleric receives to the worship of the deity. On page 40, it states that while 1st - 4th level spells are granted by the lesser servants of the cleric's deity, 5th level spells and higher are granted by the deity itself. It goes so far as to state that the cleric must supplicate the deity for the granting of these high level spells and can be judged accordingly.
This became more explicit with the publication of Deities & Demigods, by James Ward, in 1980. There is a fun little history here:

TSR - The Making and Breaking of Deities & Demigods
Gods, Demigods, & Heroes was a D&D supplement that I suggested to Gary [Gygax] and it was published in 1976. It presented gods and heroes for D&D. In those days there was no google or internet research features and so I had to do a great deal of library research to get the book done. I used the...

In the book, the delineation of spells become more clear; clerics gain 1st and 2nd level spells on their own (knowledge and faith). Then it changes up a little, depending on the "ranking" of the god. All other spells are gained through prayer.
Demigods: Grant 3rd-5th level spells directly, and the cleric cannot get higher level spells.
Lesser Gods: Grant 3rd-5th level spells through minions, grants 6th level spells directly, and cannot grant 7th level spells.
Great Gods: Grant 3rd-5th level spells through minions, and 6th and 7th level spells directly.
Suddenly, the hierarchy matters a great deal! But wait, what is this hierarchy? What does it mean?
C. I AM THE LIZARD KING! I CAN DO ANYTHING!
I am eliding the remainder to the cleric/deity section to get back to the original reason that I decided to make this quick dive into history; the review of Theros. If you wait long enough, everything comes around again. Which is why you will take my flannel shirts out of my cold, dead hands.
Anyway, the very last section of Deities & Demigods before the listing of pantheons is titled DIVINE ASCENSION. Who doesn't like the sound of that? In a nutshell, it details how a PC can be raised up to become a demi-god! And how does that happen? Well, one of the conditions is that the PC must accumulate a body of sincere worshipers. Moreover, it was already stated that "The source of a deity's godheads is in some way connected to his or her earthly worshipers, though in what manner the gods derive this power is a mystery totally beyond mortal (or immortal) comprehension. However, it is true that a god's power often increases or decreases as the number of his worshipers varies. Thus deities, and clerics as their agents, constantly try to increase the quantity and quality of their worshipers."
The combination of factors leads to the ineluctable conclusion, oft-seen in AD&D, that in a polytheistic campaign, you would have deities battling it out via proxies for worshipers, as worshipers (both in number and power) had some bearing on the deity's power, which is turn also had some bearing on the power of those that worshiped (in terms of both temporal power and the ability to cast spells).