Short answers, pulled from the story.
Helena Blavatsky was a Russian and American mystic and writer who co-founded the Theosophical Society in 1875 and became the primary founder of Theosophy as a belief system. She was born into an aristocratic family in Yekaterinoslav in the Russian Empire in 1831 and died in 1891. She preferred to be known by the initials HPB.
Helena Blavatsky co-founded the Theosophical Society in New York City in 1875, alongside Henry Steel Olcott and William Quan Judge. She served as corresponding secretary while remaining the group's primary theoretician, and she defined the doctrinal basis of the wider Theosophical movement.
Helena Blavatsky published Isis Unveiled in 1877, presenting her Theosophical worldview, and later The Secret Doctrine in two volumes in 1888 and 1889. She also wrote The Key to Theosophy and The Voice of the Silence.
Helena Blavatsky claimed she traveled to Tibet and was trained by spiritual adepts she called the Masters, Morya and Koot Hoomi, near Shigatse from late 1868 until late 1870. The claims rely entirely on her own accounts and lack credible independent testimony, and many critics and biographers have doubted them.
Helena Blavatsky was accused of producing fraudulent paranormal phenomena and of plagiarizing older esoteric sources. The 1885 Society for Psychical Research report by Richard Hodgson called her a fraud and a Russian spy, though the Society retracted those findings in 1986.
Helena Blavatsky died of influenza on the 8th of May 1891 at Annie Besant's house in London, during a flu epidemic. Her body was cremated at Woking Crematorium on the 11th of May, and Theosophists commemorate her death as White Lotus Day.