The ultimate stage of Communism is characterized by the withering away of the state. This means that in the ideal communist society, the need for a centralized government and state institutions diminishes over time. The concept of the withering away of the state is based on the belief that as communism progresses, the class struggle between the bourgeoisie (the ruling class) and the proletariat (the working class) is eliminated. Without this class struggle, there is no need for a state to mediate conflicts and maintain order.

Option 1, cultural revolution, is not the fundamental characteristic of the ultimate stage of communism, but rather a strategy used during the early stages of communist movements to challenge existing cultural, social, and political structures.

Option 2, dictatorship of the proletariat, refers to a transitional period between capitalism and communism where the working class has political power. While this is an important aspect of Marxist theory, it is not the fundamental characteristic of the ultimate stage of communism.

Option 3, formation of a World state, does not accurately describe the ultimate stage of communism. While some Marxists envision a global communist society, the formation of a World state is not a necessary condition for the ultimate stage of communism.

Therefore, the correct answer is option 4, withering away of the