Madame Helena Blavatsky, in two introductory essays, offers students of Theosophical beliefs a wide-reaching and worldly outlook on the Ancient Mysteries. While demonstrating that much like Rosicrucian and Masonic philosophy, Theosophy has, at the heart of its doctrine, the concept of a Universal Brotherhood, she by no means forgets to include numerous Eastern influences, which help set apart the distinctive path of Theosophy, from other arenas of esoteric study, while at the same time giving numerous examples of personal expression and choices, within our collective, spiritual interests.
Helena Petrovna Blavatsky (Russian: Еле́на Петро́вна Блава́тская, 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.
Any sufficiently thorough tome on the history of mysticism or the occult will have sections if not entire chapters dedicated to Helena Petrovna Blavatsky (Madam Blavatsky) and her influence on that field. She has had a huge sway on modern mystical philosophy from her own personal experiences to the founding of the Theosophical society in India.
Having no accepted creed, our society is very ready to give and take, to learn and teach by practical experimentation as opposed to mere passive and credulous acceptance of enforced dogma. It is willing to accept every result claimed by any of the foregoing schools or systems that can be logically and experimentally demonstrated. Conversely it can take nothing on mere faith no matter by whom the demand may be made. . . A theosophist is one who gives you the theory of God or the works of God which has not revelation but an inspiration of his own for its basis.
The book is a good place to start in order to understand the ideology behind Theosophy and what a Theosophist is.