https://en.wikipedia.org/wiki/Safavid_Empire

https://en.wikipedia.org/wiki/Safaviyya

It was basically just something invented, or adopted, ad-hoc by a Sufi Saint who practiced Sunnism and his followers who did not want to be under the yoke of the Ottomans any more, actually in those days this concept did not even exist and it was the 15th century already, and then the whole Shia Sunni myth was invented after the empire took power in the 15th century, like 700 years after Muhammad died.

The Fatimids existed before this in 900, around 200 years after Muhammad's death. But this empire was completely different from the Fatimids, and it came into being hundreds of years after their fall.