Bla·vat·sky 
(blə-vătskē, -vät-), Helena Petrovna Hahn 1831-1891.
(blə-vătskē, -vät-), Helena Petrovna Hahn 1831-1891. Russian-born theosophist who founded (1875) the Theosophical Society in New York City and wrote books of occult lore, such as Isis Unveiled (1877).