Mathematics, Philosophy and writing.
I mentioned in the comments:
- Charles Sanders Peirce
- W.V.O. Quine
- Bertrand Russell
- A.N. Whitehead
But also:
- Bernard Bolzano
- George Boolos
- Alonzo Church
- René Descartes
- Solomon Feferman
- Gottlob Frege
- Kurt Gödel
- David Hilbert
- Pierre-Simon Laplace
- Jan Łukasiewicz
- Blaise Pascal
- Henri Poincaré
- Hilary Putnam
- Frank P. Ramsey
- Raymond Smullyan
- Alfred Tarski
And this list omits many people who were philosophers who considered mathematics (such as Wittgenstein or Hintikka) or mathematicians who thought philosophically about mathematics (such as Brouwer) or logicians who published mathematical logic articles in philosophy journals, or mathematicians who found themselves doing early research on AI and therefore became philosophers of mind (such as Turing or Yehoshua Bar-Hillel), or a large number of scholars (such as Pythagoras, Galileo, or Newton) who lived before the modern separation of mathematics and philosophy, as well as many mathematician-philosophers who are not truly famous.
Kurt Gödel considered himself a philosopher who did mathematics, rather than as a mathematician who did philosophy. His philosophy is non-standard, and has not been taken seriously by some, but he has a Stanford Encyclopedia of Philosophy article, which makes it "official".