Marcel Proust is the author of the oft-cited, little-read six-volume novel
In Search of Lost Time. The original manuscript was written in French, and was continually altered by Proust until his death (even when he was physically unable to write any longer, he enlisted one of his nurses to carry out the necessary changes for him).
Proust is (in)famous mostly for his ceaslessly detailed descriptions of even the most mundane things or events (honestly, you can't have read this book and look at a madeline or a cup of tea in the same way as before).
Proust was quite the controversial figure of his time with his scathing description of the banalities of French artistocratic society and his clearly Pro-Dreyfus stance (the Dreyfus affair was a court case which ignited the issue of anti-semitism in Europe at the time, my knowledge of which is admittedly limited). Also, in the fourth volume, Sodom and Gommorah, Proust vividly and reverently describes a clandestine homosexual encounter between two French nobles. Proust, himself a homosexual, was ahead of his time not only in depicting homosexual acts, but in depicting them in a beautiful and frankly sensual manner.
The book also goes into GREAT depth about disappointment, lost love, the nature of friendship, and the clash between idealization and reality. It's a fabulous piece of work and I couldn't begin to do it justice in such a brief summary, but if you have enough free time to read a 4800-page novel, you won't regret it.