Universal class is a category derived from the philosophy of Hegel, redefined and popularized by Karl Marx. In Marxism it denotes that class of people within a stratified society for which, at a given point in history, self-interested action coincides with the needs of humanity as a whole.
Hegel
Hegel believed that history was a movement tending towards the realization of "freedom" – which, in his own historical moment, he had held his own society to represent, or at least represent the beginning of. For Hegel, divisions and conflicts between people were the external appearance of the internal tensions which drive the development of Spirit. Conflict and its resolution were the ratchet by which human progress was driven steadily forwards – he once famously described Napoleon Bonaparte as "the World Spirit on horseback". Accordingly: having arrived at the end of history, these divisions were to be reconciled by the new "universal class" of statebureaucrats, who acted at all times to reconcile conflicts of interest and acted only in the best interests of the entire society. He also believed in the universal class as an end product.
Marx
Marx took the Hegelian concept of a class which might act in the interests of all. For Marx, the opportunities for further human progress could be realized or lost, depending on the extent to which the universal class of the moment directed social developments. For example, the opportunities opened up by the surplus of labor in the Middle Ages could not be exploited by the feudal lords, with their system of tithes extracted from peasants in limited territories. Entrepreneurs were able to find productive uses for that labor in towns. Feudal lords gained or lost social power according to how well they accommodated this new class of people into their domains and "courts". Eventually, as European economies flourished under the social organization of the market, the entrepreneurs gradually or violently took formal control of their societies from the old class of aristocrats. In doing this the bourgeoisie sought to further its own interests, which inevitably furthered the interests of society as a whole. So, for a period, Marx characterizes the bourgeoisie as the universal class. Marx considered the universal class in his time to be the proletariat – roughly speaking, the class of persons contributing their labor to society in exchange for subsistence wages. At around the time of the various rebellions which took place across Europe in 1848, the bourgeoisie lost their position as society's avant-garde, by Marx's analysis. They had become more interested in consolidating their own social power than in revolutionizing society. The revolutionary baton had passed to the proletariat, which had both the means and the incentive to take human progress further. The moment of this transition is significant for Marxist thought in another way. As a historical materialist analysis, Marxism ought to be able to account for its own appearance at a certain moment in history, by reference to material, historical processes. The proletariat's succession to the throne of universal class provides a plausible candidate, at least within the terms of Marxist thought. It marks a new material stage, which would permit or perhaps even require there to be a Karl Marx at the level of ideas.