René Descartes was a French philosopher, mathematician, scientist and writer, known as one of the founders of modern philosophy. He is also known by his Latinized name
Renatus Cartesius. He is particularly famous for his philosophical statement, "I think, therefore I am" (Cogito, ergo sum, in Latin.
The correct pronunciation of René Descartes in French can be phonetically transcribed as
Ruh-neh Deh-cahrt. To pronounce his name correctly, the first mistake to avoid is to pronounce the "né" in René as "ney" and the "Des" in Descartes as "day". This is a typical error by English speakers. The "e" must not become an "a" sound, but it must be pronounced as a soft "e" as heard in the audio file.
In the second half of Descartes, "cartes", the final "es" is silent, so all you hear is "cart", with a very open "a" sound and a gargled "r" (like the "r" in René as well). Because that kind of "r" is so difficult for a non-native speaker to reproduce, to have a good enough pronunciation, it isn't an absolute necessity.