Skyrim: Paarthurnax Used to Be on Alduin's Side

gamerant.com:

Paarthurnax is arguably one of the most memorable NPCs in The Elder Scrolls 5: Skyrim.His wisdom and patience with the Dragonborn make him a valuable ally, and a likable character. That said, his road to becoming the dragon he is now was long and arduous.

To meet Paarthurnax, the player must progress the main storyline of Skyrim until they meet the Greybeards. After this, they will eventually let the Dragonborn meet their Grandmaster.

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“Paarthurnax” in the dragon tongue means “Ambition, Overlord, Cruelty.” This was likely an accurate portrayal of his character, as Paarthurnax once served as Alduin’s lieutenant during the Dragon War, during which he committed countless atrocities against the human race. He was also Alduin’s brother, and thus, the two shared a familial bond.

At one point, however, Paarthurnax rebelled against Alduin. He took the side of the humans and taught them how to use the Thu’um or the Voice. Some say that this change of heart was due to the divine intervention of Kyne, goddess of the Storm and mother of men and beasts. With help from Paarthurnax and other defector dragons, the humans managed to defeat Alduin. Though they did not kill him. Instead, they sent him forward in time, ensuring his inevitable return to Mundus.

After Alduin’s banishment, Paarthurnax retreated to the summit of the Throat of the World. He was still a dragon and knew that all dragons held an innate desire for power. Paarthurnax did not want to turn back to his old ways, so he isolated himself at the Throat of the World, following the pacifist teachings of the Way of the Voice. It was a philosophy developed by Jurgen Windcaller, who believed that the Voice should be used to worship the gods, and