Zoroaster (Zarathustra), the founder of Zoroastrianism, was an Iranian:

Zoroaster (Zarathustra or Zarathushtra) was an ancient Iranian prophet and religious reformer, who founded the religion known as Zoroastrianism.

About Zoroaster:

• His date is uncertain; scholars place him anywhere between about 1500 and 500 BCE (many suggest around 1200-1000 BCE).
• He lived in north-eastern Iran or Central Asia.
• He received a revelation from the supreme god, Ahura Mazda (the "Wise Lord").
• He preached against the worship of many gods and against animal sacrifice.

Teachings of Zoroastrianism:

• It is one of the oldest monotheistic (or dualistic) religions.
• The world is a battlefield between good, led by Ahura Mazda (and the spirit Spenta Mainyu), and evil, led by Angra Mainyu (Ahriman).
• Humans have free will and must choose good through "good thoughts, good words and good deeds" (Humata, Hukhta, Hvarshta).
• Fire is regarded as a symbol of purity and of Ahura Mazda, and fire temples are the places of worship.
• The dead are traditionally exposed in "Towers of Silence" (dakhmas), to avoid polluting the earth and fire.

Its sacred text:

• The "Avesta" is the sacred book of Zoroastrianism.
• The "Gathas" (hymns), believed to have been composed by Zoroaster himself, are its oldest part.
• The language of the Avesta (Avestan) is closely related to Vedic Sanskrit.

Zoroastrianism in history:

• It became the main religion of the Persian empires (the Achaemenids, Parthians and Sasanians).
• After the Arab conquest of Iran in the 7th century, many Zoroastrians migrated to India.

Zoroastrians in India (Parsis):

• They landed at Sanjan, on the coast of Gujarat, around the 8th-10th century CE.
• They are known as Parsis, and are one of the notified minority communities of India.
• Their new year is "Navroz" (Nowruz).
• Famous Parsis include Dadabhai Naoroji, Jamsetji Tata, Pherozeshah Mehta and Homi Bhabha.

Why not the other options?

• ✗Zoroaster was not a king, poet or general; he was a religious teacher and prophet.