tolkiens legendarium - Is the One Ring only loyal to Sauron or would it serve any powerful being?

I had this exchange on What would have happened if the Balrog of Moria had taken possession of The One Ring? with Jeremy French.

Jeremy French: But how would he have got it to fit?

DavRob60: That would not be a problem, as the ring has been show reducing his diameter by himself to suit Isildur finger. We could safely assume it would be able to expand again to fit the Balrog's finger. As Konrad Rudolph commented here, at the beginning of LotR, Bilbo (?) mentioned that the ring became sometimes looser and sometimes tighter.

Jeremy French: the ring changed because it wanted to fit on Isildur's finger. It would not want the balrog to challenge it's master so why would it accommodate it?

So, would the One Ring scrupulously serve a powerful being like the Balrog, Saruman or even Gandalf, or would it plot to get back to its master and ultimately betray its bearer, like it did for Isildur?

Answer

This question is quite close.

I answered with text from Letter 246:

Confrontation of Sauron alone, unaided, self to self was not contemplated. One can imagine the scene in which Gandalf, say, was placed in such a position. It would be a delicate balance. On one side the true allegiance of the Ring to Sauron; on the other superior strength because Sauron was not actually in possession, and perhaps also because he was weakened by long corruption and expenditure of will in dominating inferiors. If Gandalf proved the victor, the result would have been for Sauron the same as the destruction of the Ring; for him it would have been destroyed, taken from him for ever. But the Ring and all its works would have endured. It would have been the master in the end. Gandalf as Ring-Lord would have been far worse than Sauron. He would have remained 'righteous', but self-righteous. He would have continued to rule and order things for 'good', and the benefit of his subjects according to his wisdom (which was and would have remained great).

That seems to show that:

1. the allegiance of the Ring can change


2. but not its nature.

You ask:

So, would the One Ring scrupulously serve a powerful being like the Balrog, Saruman or even Gandalf, or would it plot to get back to its master and ultimately betray its bearer, like it did for Isildur?

So according to the quote (and my personal interpretation...), the One would try to go back to its master until its "true allegiance" was won. Once was Sauron defeated, the Ring would no longer try to join him, but he would NOT serve "scrupulously". He would still act in Sauron's image, and try to overpower and corrupt its bearer:

But the Ring and all its works would have endured. It would have been the master in the end.