Certainly, Tolkiens main unique appendices and variety of non-novel stories– a number of which were published posthumously under the editorial stewardship of his recently-passed son, Christopher Tolkien– portray Morgoth (as the character came to be understood upon his wicked turn,) as the original huge bad of Middle Earth. Morgoth waged wars against the races of Elves, Men and Dwarves on an unfathomable scale, using the might of Orc armies and monstrous allies like Balrogs, Dragons, Trolls and Giant Spiders for lots of centuries until his final defeat and exile into the Great Void, which marked completion of Middle Earths First Age. That would be the last time Morgoth would ever populate Middle Earth, although threatening prophecies foretold his return, which never eventually happened.
Thats where Sauron comes in, since the character– initially called Mairon, a Maiar (prehistoric spirits who serve the Valar)– succumbed to a desire for more power, and was thusly influenced by Morgoths evil, serving as one of his lieutenants throughout the malicious lords epoch-spanning wars. Tolkien left some of Saurons exploits open to interpretation about whether he was even truly wicked– at least throughout particular eras– and there is space for the character to manifest in a nuanced manner on the Amazon series as a Loki of sorts for Second Age Middle Earth.
While Saurons own hoax in Middle Earth spans numerous millennia, his most infamous act was, of course, the ploy that inveigled the leaders of Middle Earths races to forge and make use of the Rings of Power, which he privately controlled with the One Ring; a story that was notoriously informed onscreen with powerfully pithy dialogue from Cate Blanchetts narrating Galadriel in The Fellowship of the Rings prologue. Promising to teach types of magic that would conserve the world– maybe in case Morgoth would ever return– Sauron manipulated master Elven artisan Celebrimbor into creating the secretly-tainted Rings of Power: three to the Elves, seven to the Dwarf lords and nine to the race of Men.
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Including fuel to that concept is the reality that Peter Jackson initially had styles to utilize Sauron in his “Annatar” kind for Return of the Kings climactic Battle at the Black Gate. As you can see in the image right away above (from a behind-the-scenes documentary), the original context of the scene– set after Aragorn appears enchanted after seeing the Eye of Sauron– was that Sauron had actually become effective enough to physically manifest onto the battleground, first in his old reasonable form, after which he changes into the armored figure we saw in the prologue, and begins directly attacking.
The other viable Sauron story would be the fall of the island kingdom of Númenor, which took place a couple of hundred years after the Elves, joined by the Númenoreans, waged a very first war versus Sauron. There, Sauron, once again under the disguise of a reasonable type, insidiously ingratiated himself to the corruptible King Ar-Pharazôn, ultimately leading to the increase of Morgoth worshippers guaranteed everlasting life.
Tolkiens main novel appendices and array of non-novel stories– numerous of which were published posthumously under the editorial stewardship of his recently-passed child, Christopher Tolkien– depict Morgoth (as the character came to be known upon his wicked turn,) as the original big bad of Middle Earth. Morgoth waged wars against the races of Elves, Men and Dwarves on an abstruse scale, using the may of Orc armies and monstrous allies like Balrogs, Dragons, Trolls and Giant Spiders for numerous millennia until his last defeat and exile into the Great Void, which marked the end of Middle Earths First Age. While Saurons own trickery in Middle Earth covers numerous millennia, his most notorious act was, of course, the ruse that inveigled the leaders of Middle Earths races to forge and utilize the Rings of Power, which he covertly controlled with the One Ring; a story that was notoriously told onscreen with strongly pithy dialogue from Cate Blanchetts telling Galadriel in The Fellowship of the Rings beginning.