His great epic, the Shāhnāmeh ("The Great Book", In Persian language, Shah means king, monarch or dynast, but when it is used as a prefix, it means "Big", "Great" or "Major".), to which he devoted more than 35 years, was originally composed for presentation to the Samanid princes of Khorasan, who were the chief instigators of the revival of Iranian cultural traditions after the Arab conquest of the seventh century.
When he was just 23-years old, he found a “Shāhnāmeh” written by Abu-Mansour Almoammari; it was not, however, in poetic form. It consisted of older versions ordered by Abu-Mansour ibn Abdol-razzagh. The discovery would be a fateful moment in the life of the poet. Ferdowsi started his composition of the Shahnameh in the Samanid era in 977 A.D During Ferdowsi’s lifetime the Samanid dynasty was conquered by the Ghaznavid Empire. After 30 years of hard work, he finished the book and two or three years after that, Ferdowsi went to Ghazni, the Ghaznavid capital, to present it to the king. There are various stories in medieval texts describing the lack of interest shown by the new king, Sultan Mahmud of Ghazni, in Ferdowsi and his lifework. According to historians, Mahmud had promised Ferdowsi a dinar for every distich written in the Shahnameh (60,000 dinars), but later retracted and presented him with dirhams (20,000 dirhams), which were at that time much less valuable than dinars (every 100 dirhams worth 1 dinar). Some think it was the jealousy of other poets working at the king’s court that led to this treachery; the incident encouraged Ferdowsi's enemies in the court. Ferdowsi rejected the money and, by some accounts, he gave it to a poor man who sold wine. Wandering for a time in Sistan and Mazandaran, he eventually returned to Tus, heartbroken and enraged. He had left behind a poem for the King, stuck to the wall of the room he had worked in for all those years. It was a long and angry poem, more like a curse, and ended with the words:"Heaven's vengeance will not forget. Shrink tyrant from my words of fire, and tremble at a poet's ire."
The Shāhnāmeh (Book of Kings), or "The Great Book" consists of the translation of an even older Middle Persian work titled the Book of Lords. It has remained exceptionally popular among Persians for over a thousand years. It tells the history of old Persia before the Arab conquest of the region. This tale, all written in poetic form and in Darī Persian, starts 7,000 years ago, narrating the story of Persian kings, Persian knights, Persian system of laws, Persian Religion, Persian victories and Persian tragedies. The main source of Ferdowsi for historical and some of the mythological events was "Khodaynama", a book which was gathered and written during the Sassanid era.
“ ... I suffered during these thirty years, but I have revived the Iranians (Ajam) with the Persian language; I shall not die since I am alive again, as I have spread the seeds of this language ... ” Upon the presentation of the Shāhnāmeh, Sultan Mahmud was furious for not being the subject of the book and finally betrayed the agreement by offering Ferdowsi thirty camels loaded with Silver; the offer was refused by the poet. Heartbroken and poor the poet returned to his home town of Tus, the Sultan eventually realising his error and the true value of the Shāhnāmeh sent the agreed fee to the poet yet, upon the arrival of the camels the Ferdowsi's coffin was being carried out through the exit gate of Tus to his grave.
Ferdowsi has a unique place in Persian history because of the strides he made in reviving and regenerating the Persian language and cultural traditions. His works are cited as a crucial component in the persistence of the Persian language, as those works allowed much of the tongue to remain codified and intact. In this respect, Ferdowsi surpasses Nezami, Khayyam, Asadi Tusi, and other seminal Persian literary figures in his impact on Persian culture and language. Many modern Iranians see him as the father of the modern Persian language. According to the Encyclopedia Britannica:The Persians regard Ferdowsi as the greatest of their poets. For nearly a thousand years they have continued to read and to listen to recitations from his masterwork, the Shah-nameh, in which the Persian national epic found its final and enduring form. Though written about 1,000 years ago, this work is as intelligible to the average, modern Iranian as the King James version of the Bible is to a modern English-speaker. The language, based as the poem is on a Pahlavi original, is pure Persian with only the slightest admixture of Arabic.