Marie-Jean-Léon, Marquis d'Hervey de Saint Denys

Marie-Jean-Léon Lecoq, Baron d'Hervey de Juchereau, Marquis d'Hervey de Saint-Denys (5 May 1822–2 November 1892, Paris), was a French sinologist and man of letters, and one of the earliest oneirologists.

Hervey de Saint Denys devoted himself to the study of Chinese, and in 1851 published his Recherches sur l'agriculture et l'horticulture des Chinois, in which he dealt with the plants and animals that might be acclimatized in the West. He translated Chinese texts as well as some Chinese stories not of classical interest but valuable for the light they throw on oriental custom. He also translated some works from the Spanish, and wrote a history of the Spanish drama.

Hervey de Saint Denys has recently started to be known for his introspective studies on dreams. He wrote down his dreams on a daily basis from the age of 13. In 1867, he anonymously published Les rêves et les moyens de les diriger; observations pratiques (Dreams and the Ways to Direct Them:Practical Observations). In this book, he proposed techniques to control dreams, and he described dreams in which the "dreamer is perfectly aware he is dreaming". This particular state of consciousness later came to be called lucid dreaming.

At the Paris Exhibition of 1867, Hervey de Saint Denys acted as commissioner for the Chinese exhibits; in 1874 he succeeded Stanislas Julien in the chair of Chinese at the Collège de France; and in 1878 he was elected a member of the Académie des Inscriptions et de Belles-Lettres. He died in Paris on the 2nd of November 1892.