A sovereign ruler is the member within a sovereign community who has established the objectives for the sovereign community and the rules that govern how those objectives will be achieved.
For example, parents are the sovereign rulers within the family because they call the shots. They determine the direction the family is headed and the rules that will get it to its objectives. The direction, objectives and rules are not always explicit, but they exist never-the-less.
Modern thinkers struggle with the notion of a "sovereign ruler", because it brings with it other notions such as imposition, submission, rewards and punishment. They lose sight of the fact that sovereign rulers call the shots because they possess the wherewithal needed to create good (a state of harmony).
Sovereign rulers are a fact of life. Wherever we are and whatever we do, we are subject to the approval or disapproval of those who have sovereign authority over us. Of course, we are free to make efforts in a different direction to the one chosen by the sovereign ruler, but we shouldn't be deluded in imagining that it will not be met with corresponding effort to persuade us to reassess the wisdom of the course we wish to pursue. Again, this is as it should be because we are needy of the things the sovereign ruler provides.
The idea of being needy is another notion that modern thinkers struggle with. However, as children we are needy of the necessities of life - food, clothing, shelter and nurture - that our parents provide. As citizens, we are needy of basic infrastructure - roads, power, water, hospitals, transportation, communication, waste disposal, etc - that our governments provide. We have grown so accustomed to demanding that our needs be met that we have lost sight of how insignificant we really are in the scheme of things. What a horrible prospect to have to go "cap in hand", "on bended knee" as it were, to appeal to the sovereign ruler for consideration of a particular need.