The Seljuks

Iran, like Western Europe, emerged at the beginning of the first millennium AD from a period of major disorder into one of minor discord; the promise of relative stability engendered a great age of building. And it is with the name of this and the succeeding dynasties that Islamic architecture in Iran is associated.
The Seljuks, like their successors, came from the northeast. They were members of a Turkish-speaking tribe from Turkistan, known as Ghuzz, and were early converted to orthodox Muhammedanism, that is to say Sunnism. Their first act of conquest was to seize Marv from the Ghaznavids, and by 1043 they were firmly established in Khorassan. Twelve years later their leader, Toghrol Beg, entered Baghdad and was named "Vice-regent of the successor of the Prophet and Lord ofall the Muslims" by the Caliph. His successors were Alp Arsalan (1063-72), Malik Shah (1072-92), and Sultan Sanjar (1096-1157). Alp Arsalan conquered Asia Minor and made several successful expeditions against the Greeks; he is said to have had such long mustaches that they had to be tied back when he was shooting. Both he and his son Malik Shah owed much to the wise counsel and energy of their vizier, Nol-Molk, the patron of OmaKhayyam.
Order was never completely established in the Seljuk dominions. The family itself was rent by internal strife -there were separate, and sometimes rival dynasties in Kerman and Iraq. They completely failed to check the growing power of the Assassins, who were responsible for the murder of Nizam ol-Molk and possibly also of Malik Shah.