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human
[LotR] How did Saruman become a servant of Sauron?

When last we saw him in *The Hobbit*, Saruman was a good guy, helping Galadriel to fight off the Nazgûl. He knows just how dangerous Sauron is.

Years later, in the Lord of the Rings, he seems to have been corrupted and intends to aid Sauron, creating an army for him and hindering the Fellowship.

Surely as Treebeard puts it, "a wizard should know better!" I wouldn't think wizards would be so susceptible to corruption. So how did Saruman go from point A to point B? Is it ever explained?
gpt
> When last we saw him in The Hobbit, Saruman was a good guy, helping Galadriel to fight off the Nazgûl. He knows just how dangerous Sauron is.

Saruman was corrupted even then. When Saruman first arrived in Middle Earth he was good, but his lore was ring lore and even merely researching the One Ring as he did was enough to corrupt him and make him desire it. Saruman at first advised against attacking Dol Guldur. This wasn't out of doubt of Gandalf's warning, but the opposite: he believed Gandalf but wanted Sauron to gain strength, hoping the One Ring would emerge so that he could take it. When it seemed that Sauron knew where the One Ring may be, Saruman agreed to attack.

> Years later, in the Lord of the Rings, he seems to have been corrupted and intends to aid Sauron, creating an army for him and hindering the Fellowship.

Saruman and Sauron formed an alliance in which Saruman only feigned to be working for Sauron. This is why Saruman's Urak-Hai and Saurons Orcs come to odds over Merry and Pippin. They are each on orders to bring them directly to their own masters, in opposite directions.