The True Master.

[Gurthang]

I've been thinking on this for a time now. I will keep it short though.

Sauron makes the ring, as everyone knows, and pours much of his power into its creation. Once he is separated from his Ring, he loses much of his power and can't even take on physical form. He now requires his Ring to do much of anything.

Now, let me restate that. Sauron, without his Ring, is almost nothing. On the other hand, his Ring has an immense will to conquer whoever bears it. We can see this in Isildur, Gollum, Bilbo, and Frodo. It is also said, I'm not sure where, that if one of the Wise could have used the Ring (Gandalf, Elrond) it would in the end overpower even them and just make them an image of what Sauron was. Which makes sense, the Ring's will is Sauron's will, so under its direction a being becomes like to Sauron.

I suppose you can see where this is going. Sauron needs his Ring to do much of anything. He must have it; it is part of him; he searches for it; he sends his mightiest servants to get it back. In short, the Dark Lord is very much like Gollum. Both have been conquered by the Ring and reserve very little in their rush to retrieve it. It consumes them.

The Ring dominates, consumes, conquers, overpowers, masters. It cannot be resisted. It is uncontrollable, even by it's 'master'. So, the Ring is the True Master.