Most people these days don't take the time to read and learn about the old great philosophers. They might be able to give you some names, but chances are would be able to to tell you very little about why they are important and what were their key philosophies. It's ironic how little people think about Descartes when he was the man who shaped the way we think today.
While Rene Descartes made a great contribution to mathematics and geometry, perhaps his most influential work was his desire to explain the mysteries of the universe in mechanistic terms. His promotion of dualism led scientists to approach previously unsolvable mind-body problems, and initiating a second wave of desire and ability to obtain scientific proof to that promotes, not only the existence of God and the spiritual realm, but God as a scientist.
The philosophical theories put forward by Descartes in 'Meditations' still form a key part of the syllabus on most philosophical courses at both school and university level across the world. Descartes is often credited with being the father of the dualist theory of consciousness and his thoughts are still an active part of the dualist vs materialist debates until this day.
Rene Descartes is a name still known by many today because of his work, that shows the impact he had. It wasn't just his immediate impact, lots of other subsequent philosophy in the Western world is a follow on from what Descartes has said. This means his real impact was a lot further than when he was alive, thats why I think he was of such high importance.
Imagine if an evil daemon had decided to create all your senses around you in order to trick you. Decartes may exist in the reality which this daemon created, but objectively may not. We can't be sure so we must assume that he never existed. If we do say that he existed, then we would be feeding into the daemon's lie.