Do you know what they did to Islam?
They believe in one God, the Zartosht most probably may have been a Prophet with a divine book. However, like all others, Zoroastrians fell victim to clergy and rule of emperors and kings. They believed that King is son of God. They did convert to Islam, yes, but they did not leave their past beliefs and rituals behind, just imagine how successfully they have made iran holy, not for people in iran but for other Muslim countries as well. Most of our "Islamic history" that we believe as "Islamic history" is basically these people making it what they wanted it to be. The story of Karbala is story of one of their own past prince, the religious tombs and sites are actually past holy sites given Islamic colors and names.
It truly is very interesting.
They have a history, were an empire once, still are proudful people. But they were defeated and conquered by people who they always thought inferior, wildlings and weak.