Complex sentence: Thus, in historical development the Great Leader is the leading force of the working class; he is a flawless, incorruptible human being who never makes mistakes, is always benevolent and rules for the benefit of the masses.
Split into simpler sentences: Thus, in historical development, it is the "Great Leader" who is the leading force of the working class. The "Great Leader" is also a flawless human being, who never commits mistakes, who is always benevolent, and who always rules for the masses.