An ideology is an organized set of ideas and ways of understanding the world, usually normative, and often on political, economic, ethical or philosophical subjects. Some ideologies are self-declared (e.g. environmentalism or libertarianism), while ideology is also used (often pejoratively) to refer to an unconscious set of ideas, practices and beliefs that are characteristic of a particular group but which are not held openly - for instance, many critics of capitalism think of it more as an unconscious delusion or a box which a person cannot think outside of. Marx, for instance, sees social ideology as being a superstructure that is heavily determined by the economic base of a particular society, rather than as something that is freely chosen.
An ideology, in and of itself, may not be adequate for governance, but political scientists distinguish an ideology from political philosophy in that ideology potentially can be used in governance. For example, Marx and Engels produced a political philosophy, but Lenin produced a workable ideology. "The purpose of an ideology is not to arrive at truth, but rather to perform political tasks such as creating consensus." In some cultural contexts, there may be a shared belief system, such as Japanese kokutai, which leads to something closer to ideology, such as Japanese militarism and its variants in the Control Faction and Imperial Way Faction.
Actual governance does not require ideology. A ruler such as Adolf Hitler derived his authority from personality and charisma rather than a strict ideology.  In other words, Nazi ideology was what Hitler believed. There certainly were concepts within his world-view that were ideological, such as the Nazi race and biological ideology or Lebensraum, but his judgment was supreme. The distinction between charismatic and ideological leadership of totalitarian regimes began roughly the in the mid-1970s, and later writers, such as Alan Bullock, continue to explore it; there has been a resurgence of interest in historical writing about Hitler, sometimes in comparison with other dictators such as Josef Stalin.
A ruler such as Stalin was not especially charismatic, and, while not strictly bound by ideology, still worked in a bureaucratic governance system affected by ideology. In post-WWII Soviet government, with leaders without the personal dominance of Stalin, the Party Ideologist, especially Mikhail Suslov, had a major role, never himself being likely to rise to the top position, but often being the kingmaker.
"Most ideologies, precisely because of their purposes, are non-falsifiable, circular in logic, and dependent upon image-producing metaphors. Just as the uncritical incorporation of ideology into scientific theory can lead to bad theory, so too can the uncritical incorporation of ideology into policymaking lead to bad policy."
- Woodruff D. Smith (February 1980), "Friedrich Ratzel and the Origins of Lebensraum", German Studies Review 3 (1): 51-68
- Joseph Nyomarkay (1967), Charisma and Factionalism in the Nazi Party, University of Minnesota Press, p. 12
- Alan Bullock (1992), Hitler & Stalin: Parallel Lives, Alfred A. Knopf, ISBN 0-394-586-1-9