Henry Steel Olcott (1832-1907) was an American military officer, journalist, lawyer, Freemason and the co-founder and first president of the Theosophical Society. He was the first well-known American of European ancestry to make a formal conversion to Buddhism. His subsequent actions as president of the Theosophical Society helped create a renaissance in the study of Buddhism and Oriental religions. On the evening of January 14, 1882, Olcott delivered a public lecture on "The Spirit of the Zoroastrian Religion" at Bombay Town Hall. We now offer our readers the full text of that lecture, as published in 1885 in the volume Theosophy, Religion and Occult Science. These reflections and considerations by Olcott undoubtedly constitute one of the most interesting expositions of Zoroastrianism and Zoroastrian spirituality.