Zoroastrianism is the religion and philosophy based on the teachings ascribed by the prophet Zoroaster (Zarathustra, Zartosht). Mazdaism is the religion that acknowledges the divine authority of Ahura Mazda, proclaimed by Zoroaster.
As demonstrated by Zoroastrian creed and articles of faith, the two terms are effectively synonymous. In a declaration of the creed — the Fravarānē — the adherent states: "…I profess myself a devotee of Mazda, a follower of Zarathustra." (Yasna 12.2, 12.8)
While Zoroastrianism was once the dominant religion of much of Iran, the number of adherents has dwindled to not more than 200,000 Zoroastrians worldwide, with concentrations in India and Iran.
Along with Old Persian, Avestan is one of the two oldest Iranian languages of which we have evidence (see also classification, below). The Avestan language should not be confused with the Avestan alphabet, which is a significantly later invention.
Tiridates I (Armenian: Տրդատ Ա, EA: Trdat I, WA: Drtad I) was king of Armenia beginning in 53 AD and the founder of the Arshakuni Dynasty, the Armenian line of the Arsacid Dynasty. His early reign was marked by a brief interruption towards the end of the year 54 and a much longer one from 58 to 63. In an agreement to resolve the Roman-Parthian conflict in and over Armenia, Tiridates (who was the brother of Vologases I of Parthia) was crowned king of Armenia by the Roman emperor Nero in 66 AD; in the future, the king of Armenia was to be a Parthian prince, but his appointment required approval from the Romans. Even though this made Armenia a client kingdom, various contemporary Roman sources thought that Nero had de facto ceded Armenia to Parthia.
In addition to being a king, Tiridates was also a Zoroastrian priest and was accompanied by other magi with him on his journey to Rome in 66 AD. This is about the same time that the Gospel of Matthew recorded a journey of wise men from the east to the infant Jesus in Bethlehem. This may lay behind the later Christian legend of the Three Magi. In the early 20th century, Franz Cumont speculated that Tiridates was instrumental in the development of Mithraism, which—in Cumont's view—was simply Romanized Zoroastrianism. This "continuity" theory has since been collectively refuted.