For an intriguing spin on this, look into Manichaeism, a 3rd-century religion from modern Iran which syncretizes Zoroastrianism, Christianity, and Buddhism, and

For an intriguing spin on this, look into Manichaeism, a 3rd-century religion from modern Iran which syncretizes Zoroastrianism, Christianity, and Buddhism, and survived until the middle of the last millennium in China.