This period was across Shia and Sunni dynasties through to the Mongol governance. Iran participated with its own scientists and scholars. Additionally the most important scholars of almost all of the Islamic sects and schools of thought were Persian or lived in Iran including most notable and reliable Hadith collectors of Shia and Sunni like Shaikh Saduq, Shaikh Kulainy, Muhammad al-Bukhari, Muslim ibn al-Hajjaj and Hakim al-Nishaburi, the greatest theologians of Shia and Sunni like Shaykh Tusi, Al-Ghazali, Fakhr al-Din al-Razi and Al-Zamakhshari, the greatest Islamic physicians, astronomers, logicians, mathematicians, metaphysicians, philosophers and scientists like Al-Farabi and Nasir al-Din al-Tusi, the Shaykhs of Sufism like Rumi, Abdul-Qadir Gilani – all these were in Iran or from Iran. And there were poets like Hafiz who wrote extensively in religious themes. Ibn Sina, known as Avicenna in the west, was a polymath and the foremost Islamic physician and philosopher of his time. Hafiz was the most celebrated Persian lyric poet and is often described as a poet's poet. Rumi's importance transcends national and ethnic borders even today. Readers of the Persian and Turkish language in Iran, Azerbaijan, Turkey, Afghanistan, Tajikistan and Uzbekistan see him as one of their most significant classical poets and an influence on many poets through history. In addition to individuals, whole institutions arose – Nizamiyyas were the medieval institutions of Islamic higher education established by Nizam al-Mulk in the 11th century. These were the first well-organized universities in the Muslim world. The most famous and celebrated of all the nizamiyyah schools was Al-Nizamiyya of Baghdad (established 1065), where Nizam al-Mulk appointed the distinguished philosopher and theologian, al-Ghazali, as a professor. Other Nizamiyyah schools were located in Nishapur, Balkh, Herat, and Isfahan. While the dynasties avowed either Shia or Sunni, and institutions and individuals claimed either Sunni or Shia affiliations, Shia–Sunni relations were part of Islam in Iran and continue today when Ayatollah Khomeini also called for unity between Sunni and Shia Muslims. Sunni Islam Sunni Muslims are the second-largest religious group in Iran. Specifically, Sunni Muslims came to power in Iran after the period when Sunni were distinguished from Shi'a by the Ghaznavids who ruled Iran from 975–1186 AD, followed by the rule of the Great Seljuq Empire and the Khwarazm-Shah dynasty which ruled Iran until the Mongol invasion of Iran. Sunni Muslims returned to power when Ghazan converted to Sunni Islam. About 9% of the Iranian population