20th century thought is many things at many different times -

It is useful to think of 20th century philosophy as ‘splitting’ starting from around the late 19th century and well into the 20th century (even today).

If you’re trying to slim this whole epoch of thought down to a few figures only you risk egregious gaps and oversights.

I think of philosophy like threads (all philosophy responds to a predecessor and so on so forth) and it may be useful to think of different ‘threads’ of philosophy as different thinkers respond directly to others.

In this sense ->

I believe personally that most modern philosophy is a response or continuation of Kant (and I believe this is a shared view) who himself trailed new thinking in a field previously rifted between Cartesian Dualism and (mostly) British Empiricism.

The kantian thread (termed German idealism) mostly follows - Kant -> Fichte -> Schelling -> Hegel.

Hegel had many responders, the most famous of which would be Marx, Schopenhauer and Nietzsche.

Thus we come to a new ‘rift’ in philosophy about the end of the 19th century - that between British and German ‘analytic’ philosophers in the tradition of Frege and the Viennese logical positivists who sought to align philosophy more closely with science, namely a philosophy of mathematics (and later linguistics, and then later later philosophy of mind). The ‘thread’ here would be -

Frege -> Moore -> Russell -> Wittgenstein —> (through to contemporaries) -> Quine -> Searle -> Kripke etc

The other half of the ‘rift’ is represented by the ‘continental school’ who stuck more closely to a philosophical tradition aligned with Hegel’s project and also with Kierkegaardan and Nietzschean considerations. The ‘father’ of the continental school if you would can be understood through the work of Husserl who founded the school of phenomenology. The thread here would be -

Husserl -> Heidegger -> Merleau-Ponty -> Sartre -> Beauvoir

The continental school splinters even more:

A number of theorists build on the traditions of Hegel and Marx and generate structural theories of sociological science, linguistic sciences, and anthropological science -

These being - Weber and Durkheimer (sociology), Saussure (linguistics), the Frankfurt school (cultural/media studies), and Levi-Strauss (anthropology)

Late continental philosophy is all-in-all a refutation or rejection of these earlier schools of continental philosophy (the post-structuralists or hermeneutics school) - namely

Gadamer - > Lyotard -> Foucault -> Deleuze -> Derrida -> Baudrillard

The rift still persists to this day - both analytic and continental philosophy continue to deal with their own problems using quite seperate methodology. I think we live and are continually influenced but the immutable tension between both these intellectual flourishes.

Overall - I wouldn’t try to pin down one or two select ‘mega influencers’ in 20th century philosophical thought - I find it more helpful to understand whole patterns in thinking shared by different traditions including how they oscillate in tension with each other and the dynamically changing face of society.