S. A. Kapadia 
The Teachings of Zoroaster [EPUB ebook] 

Zoroaster , also known as
Zarathustra , was a religious reformer and the spiritual founder of
Zoroastrianism . He founded the first documented
monotheistic religion in the world and also had an impact on
Plato ,
Pythagoras , and the
Abrahamic religions , including
Judaism ,
Christianity , and
Islam . Zoroastrians believe that he was a prophet who transmitted God’s messages and founded a religious movement that challenged the existing traditions of ancient Iranian religion, while in the minority Ahmadiyya branch of Islam and in the Baháʼí Faith, he is also considered a prophet. He was a native speaker of Avestan and lived in the eastern part of the Iranian plateau, but his exact birthplace is uncertain.