Zoroastrianism is a small religion with about 140,000 members. Yet its importance to humanity is much greater than its current numbers might suggest, because:
Their theology has had a great impact on Judaism, Christianity and other later religions, in the beliefs surrounding God and Satan, the soul, heaven and hell, savior, resurrection, final judgment, etc.
It is one of the oldest religions still in existence,
It may have been the first monotheistic religion.
The religion was founded by Zarathushtra (Zoroaster in Greek; Zarthosht in India and Persia). Conservative Zoroastrians assign a date of 6000 BCE to the founding of the religion; other followers estimate 600 BCE. Historians and religious scholars generally date his life sometime between 1500 and 1000 BCE on the basis of his style of writing.
He lived in Persia, modern day Iran. Legends say that his birth was predicted and that attempts were made by the forces of evil to kill him as a child. He preached a monotheism in a land which followed an aboriginal polytheistic religion. He was attacked for his teaching, but finally won the support of the king. Zoroastrianism became the state religion of various Persian empires, until the 7Th Century CE.
When Muslim Arabs invaded Persia in 650 CE, a small number of Zoroastrians fled to India where most are concentrated today. Those who remained behind have survived centuries of persecution, systematic slaughter, forced conversion, heavy taxes, etc. They now number only about 18,000 and reside chiefly in Yazd, Kernan and Tehran in what is now Iran. The 1991 census counted 3,190 Zoroastrians in Canada. The actual number is believed to be much higher.