P.Ya. Chaadaev (1794-1856), an outstanding Russian thinker and publicist, published only one of his works during his lifetime - the first letter of the Philosophical Letters, after which he was declared crazy and deprived of the right to publish. Nevertheless, Chaadaev had a powerful influence on Russian thought and literature of the 19th century. Pushkin, Herzen, Tyutchev, Zhukovsky wrote about him and referred to him. Chaadaev was compared to Pascal and La Rochefoucauld. Deep intelligence, honor and active love for Russia illuminate the legacy of P. Ya. Chaadaev, leaving him a relevant Russian thinker for the modern reader.