This is a theory put forth by an SG reader. I made a few minor edits for clarity.
TLDR: We know that Bran is Sauron from the nature of A Song of Ice and Fire. ASOIAF is the Satanically-inverted Lord of the Rings, so the winner, by definition, has to be Sauron. QED.
Leaving that aside, let’s look at Bran as Sauron using LOTR, the Silmarillion, the Appendices, the Bible, and vampire lore. When we look at Bran as Third-Age Sauron we have to see him as inverted from the Dark Lord all-seeing eye in the movies. We also have to see Bran as Second-Age Sauron, aka Annataur.
Second Age Sauron is a very seductive figure who Tolkien writes as the Antichrist from the Book of Revelation. Also keep in mind that vampires are a representation of the Antichrist . Now that we’ve laid that ground work, let’s look at how we know that Rape Rape made Bran and the Three-Eyed Raven (3ER) into a combination of Sauron and The One Ring.
The Wall and the Land Beyond is the inverted Mordor. Mordor is fire and ash. The land beyond The Wall is a world of ice. The White Walkers are the Black Riders. The Wall is the Mountains of Shadow and the Ash Mountains which were either raised by Sauron himself or by Morgoth as a fortress against the world. The Wall was raised to protect the world from the Three-Eyed Raven. 3ER’s cave is Barad Dur. We see Sauron watching the whole world from Barad Dur and 3ER watches the whole world from his cave and sends out emissaries from his cave.
Bran/Sauron as vampire: In ASOIAF, in the Cave Bran eats acorn paste which is highly likely the ground up remains of his friend Jojen Reed. This was done to turbo-charge his powers. This is vampiricism of Bran consuming his friend to gain more power. This is likely also some kind of satanic Eucharist, to use the Catholic term which is appropriate here.
Sauron was portrayed as a vampire in The Silmarillion. When he was defeated by Luthien, Sauron turned into a bat and flew away. Bran also sacrificed others so he could live. We saw Bran sacrifice Hodor and Bran sacrifice a whole freaking army at the Battle of the Long Night. These are the actions of Sauron, who loves to sacrifice other to advance his agenda
Sauron uses the Palantir to spy on the whole world. Likewise Bran uses the weirwood trees and ravens to spy on the whole world, and likely cause chaos as well.
More of Bran as a vampire. Bran with 3ER had to be invited into the world of the living when they were permitted to enter Castle Black from the land beyond just like how vampires have to be invited in. This has correlation to Sauron in the Second Age where first he disguised himself as Annataur, the Lord of Gifts to Celebrimbor in Eregion. He presented himself as wise and beautiful. Annataur just wanted to “heal the world” aka “Tikkun Olam” from the damage of the War of Wrath at the end of the First Age. He always provided the Noldor with hidden knowledge.
Sauron/Annataur used this hidden knowledge that he provided to pit Celebrimbor against Galadriel and divided the Elves to prevent them from uniting before he destroyed Eregion. Sauron used the same trick against the usurper king of Numenor at the end of the Second Age. He allowed himself to be taken prisoner to Numenor where he corrupted the king and people.
Bran is the inversion of Annataur. Annataur cloaked himself in beauty, wisdom and hidden knowledge. Bran cloaked himself in weakness, autism, false humility and hidden knowledge. Bran uses his hidden knowledge to pit people against each other. The best example is how he used his hidden knowledge of Jon’s true identity to pit him against Dany. This was a major cause of driving Dany mad and making her burn King’s Landing, delegitimizing Jon as a contender to the throne and paving the way for Bran’s ascension to total power
In conclusion, Bran’s actions are Sauron’s action. Bran acts as vampire, Lord of Gifts and pathetically inverted Dark Lord in Martin’s satanically-inverted manner. But it’s all good because Rape Rape approves of Bran’s tax policy.