The German philosopher whose dialectical idealism — the idea that history unfolds through the conflict and resolution of opposing forces, driven by the development of Spirit toward freedom — shaped Marx, Nietzsche, existentialism, and 20th-century political thought more profoundly than almost any other thinker.
Hegel argued that history has a direction and a logic: it moves through conflict toward freedom, and every age contains the seeds of its own overcoming. Marx took this and turned it upside down. Nietzsche reacted against it. The 20th century's great ideological conflicts — liberalism versus Marxism, nationalism versus cosmopolitanism — were fought largely in Hegelian terms. When Francis Fukuyama declared 'the end of history' in 1989, he was explicitly invoking Hegel.