The True Master.

[Gothmog]

Although, if you then assume the fact that the Ring's main power was in controlling or dominating other wills, it could mean that Sauron put much of his (limited) self-controlling power into the Ring. This would make me wonder if it didn't weaken his own, thus giving the Ring more dominating power than it's maker.

Interesting thinking, but is the power of self-control the same as the power to dominate others? Or is it possible that Sauron, though a lack of self-control, was able to control other's as the Ring was?

The lack of self-control shown by Sauron is more depending on his pride, his greed and lack of feelings for other living beings. It's not the power of his will that is to weak, but he doesn't have the will to stop himself, he rather enjoys not stopping himself...

Sorry, I don't have time to fully explain my thoughts about this, but I'll hopefully be back soon...