One important aspect of maintaining power by a king, dictator or religious leader is to convince a large portion of the society to believe that the ruler has some special authority to rule. Traditionally, this has been accomplished through a claim that the ruler has been given authority from God to rule.

This is most obvious in a theocratic system like present day Iran. While there are many secular officers in the system, under the Iranian constitution ultimate authority rests with the religious leaders, who assert authority from God. http://www.nyulawglobal.org/globalex/Iran.htm

Traditionally, Kings have also claimed authority from God. It may have been in connection with authority granted from a particular religion like the Catholic Church. In the case of Henry VIII in England, Henry VIII felt compelled to start his own Church after breaking with the Catholic Church. With the Emperor of Japan and Pharaohs of Egypt, the claim was that they were Gods.

Even with dictators who do not assert a belief in God, they often develop near substitutes. Ideology can often substitute for religion and leaders are often elevated to near gods. In the USSR, Lenin and Stalin were in essence raised to god status. In North Korea, they tell all kinds of tales about the miraculous act of Kin Jung Il.

The more true believers in the society, the easier it is to maintain power. In his book "The Case for Democracy," Natan Sharansky (former Soviet dissident and current Israeli politician) argues that the populations of countries run by illiberal regimes can be divided into three categories: 1) the true believers, 2) the fence sitters, and 3) the dissidents. He explains that the membership of these groups is not static, but is constantly shifting. The larger the true believer group, the more likely it is that the fence sitters will also stay in line and the easier it is to maintain power. However, the stronger the dissident group becomes, the more likely it is that the flense sitters will begin opposing the government and the harder it is for the ruler to maintain power. http://en.wikipedia.org/wiki/Natan_Sharansky