the lord of the rings - What were Saruman's original intentions, and how did they change over time?

The discussion sparked by this question led to a suggestion that I open a separate question on a related subject. Sauron started out good, became bad, briefly repented, the went full-on evil. Saruman too started out as a good guy, but very gradually turned to the Dark Side, so to speak.

I know some of the factors which contributed to his slow decline - jealousy of Gandalf, gradually increasing egotism, corruption at the hands of Sauron via the Palantir, and so on. And I know - in part because of the answers to this question - what Saruman's intentions were during the events of The Lord of the Rings: basically, he wanted to pretend he was Sauron's buddy for as long as it was profitable to do so, steal the Ring, use it to defeat his enemies (including Sauron), and eventually take Sauron's place (which, whether or not this was Saruman's intention, would automatically make him the baddest baddie in Middle-earth).

But I know little (aside from what I have already mentioned above) about what his intentions were from the time he came to Arda to the time Gandalf located the One Ring, how soon they began to change, and why.

What were Saruman's original intentions, how soon did he begin to stray, and what started that process?

Answer

Saruman's downfall seems to have come as a result of his study of the works of Sauron, and the subtle realisation that his abilities (and the essence of his power) were actually pretty comparable to his own. In the Silmarillion, Tolkien makes it crystal clear that he was already corrupted by the time of the first White Council, shortly after the first defeat of Sauron's forces;

Then the White Council was summoned; and Mithrandir urged them to swift deeds, but Curunír [Saruman] spoke against him, and counselled them to wait yet and to watch. ‘For I believe not,’ said he, ‘that the One will ever be found again in Middle-earth. Into Anduin it fell, and long ago, I deem, it was rolled to the Sea. There it shall lie until the end, when all this world is broken and the deeps are removed.' Therefore naught was done at that time, though Elrond's heart misgave him ... Thus the Wise were troubled, but none as yet perceived that Curunír had turned to dark thoughts and was already a traitor in heart: for he desired that he and no other should find the Great Ring, so that he might wield it himself and order all the world to his will. Too long he had studied the ways of Sauron in hope to defeat him, and now he envied him as a rival rather than hated his works. And he deemed that the Ring, which was Sauron's, would seek for its master as he became manifest once more; but if he were driven out again, then it would lie hid. Therefore he was willing to play with peril and let Sauron be for a time, hoping by his craft to forestall both his friends and the Enemy, when the Ring should appear.

_{The Silmarillion; OF THE RINGS OF POWER AND THE THIRD AGE}