Great question.
My joke answer is: probably Hegel but I don’t know for sure because he’s too difficult for me to understand.
My serious answer is Graham Priest, a philosopher and logician who has written extensively on paradoxes, non-classical logics, metaphysics, and theories of intensionality. His books are extremely technically demanding, but he is an excellent writer. To the extent that I’ve managed to understand what he is saying it has improved my thinking a lot. He is one of those thinkers who is simultaneously extremely big picture and also being super rigorous in the details and argumentation.
Ever since I first studied formal logic in my first year of undergrad, I always felt it had promise for clarifying our thinking. Unfortunately, in the next decade of my academic education in philosophy I was disappointed on the logic front. Logic seemed either irrelevant the questions I was concerned with or, when it was used, it seemed to flatten and oversimplify the important nuances. Discovering Priest’s books (a decade after I’d left academic philosophy) fulfilled my youthful dreams of logic as a tool for supercharging philosophy. Priest uses the formalisms of logic like an artist to paint wonderous and sometimes alien philosophical landscapes.
Books by Priest in suggested reading order:
An Introduction to Non-Classical Logic: From If to Is. Cambridge University Press, Second Edition, 2008.
It’s a great reference. You don’t need to read every page, but it is very helpful to turn to when trying to make sense of the rest of Priest’s work.
Beyond the Limits of Thought. Oxford University Press, Second (extended) Edition, 2002.
Presents the surprisingly central role of paradoxes throughout the history of philosophy.
The unifying theme is Priest’s thesis that we humans really are able to think about the absolute limits of our own thought in spite of the fact that such thinking inevitably results in paradoxes.
One: Being an Investigation into the Unity of Reality and of its Parts, including the Singular Object which is Nothingness. Oxford University Press, 2014.
A study in the metaphysic of parts and wholes
A deeply counterintuitive but surprisingly powerful account based on contradictory entities
Towards Non-Being, 2nd (extended) edition. Oxford University Press, 2016.
An analysis of intensional mental states based on a metaphysics of non-existent entities.
Science and Sanity looks pretty interesting. In the book summary it says he stressed that strict logical identity doesn’t hold in reality. Can you say more about how he builds up a logical system without using the law of identity? How does equational reasoning work for example?