Helena Petrovna Blavatsky (Russian: , Yelena Petrovna Blavatskaya, often known as Madame Blavatsky; 12 August [O.S. 31 July] 1831 8 May 1891) was a Russian occultist, philosopher, and author who co-founded the Theosophical Society in 1875. She gained an international following as the leading theoretician of Theosophy, the esoteric religion that the society promoted.