Who is Fernand Gregh from How Proust Can Change Your Life ; Not a Novel and what is their importance?

Gregh was a man who wrote a disparaging comment about one of Proust's book in a local periodical. Gregh then asked Proust to review his own work. Proust wrote a wicked note about the book, but thought better of sending it and what Proust did send to Gregh was glowing and laudatory. This episode demonstrates an ideal approach to friendship according to author De Botton.