. The Pre Socratics with the question how is change possible? After all what is already is. And what is not is nothing and can not be made into an "is". For it to become an is it already has to be something. This led up to Plato who said the realm of the Is is one realm--the true realm. The world we are in --the changing world is the world of change. Then came Aristotle and Plotinus and after that it took some time to sort things out.
Then the Middle Ages with the question of faith with reason. in the world of Torah it was Saadia Gaon who combined them. After him everyone accepted that a synthesis of faith with reason is the proper way of Torah.
The proper approach here also was unclear and all Torah thinkers were going with Plato until the Rambam who turned to Aristotle. The remainder of the Middle Ages was simply to clear up the loose ends.
Then began the Mind Body problem with Descartes. This question has two approaches to it. One from John Locke. He was the beginning of the empirical approach to this. i.e. the mind --reason--abstracts from the senses. That is how it gets to pure reason. By this process of abstraction. [Hume went on this path after Locke.] Then the Rationalists- Spinoza, Leibniz. Berkeley was a radical version of this holding that all we know is what is in our own heads.
Kant published two versions of the Critique of Pure Reason. He treads a middle path where there is a ground of validity of pure reason--but only within the confines of conditions of possible experience. -not actual experience. Then came the neo-Kant people that understood Kant in different ways and modified him. That would be Fichte and Hegel on the side that reason can go into the thing in itself (dinge an sich). Then Fries on the side of immediate (not through anything) non intuitive (not by the senses) knowledge --a kind of third source of knowledge.
In any case after Kant people were either trying to figure him out and also Hegel. Picking up the loose ends so to speak. The World War One came and everyone abandoned Kant and Hegel and anything German. So the 20th century was a lot of mediocre people making up profound sounding stuff. As John Searle said about 20th century philosophy "It is obviously false."
Like there was one girl listening to Sartre talking how words mean on thing for the person talking but something else for the one listening. So a twelve year old girl asked him "So why are you talking?"
Dr Kelley Ross considers the Kant Fries School as a kind of continuation of Plato.
. Hegel to me seems to be also a kind of continuation of ancient Philosophy Plotinus in particular. At least consciously Hegel was giving a defence of Christianity though many took his ideas in the opposite direction. I think in some way that Hegel went even beyond Aquinas in this sense. That with Aquinas he got everything to fit together (as a large puzzle). But with Hegel, the pieces all are interconnected as an organic whole.