Abu'l-Qâsem Ferdowsi Tusi (also Firdawsi, Persian: ابوالقاسم فردوسی توسی; 940 – 1019/1025) was a Persian poet and the author of Shahnameh ("Book of Kings"), which is one of the world's longest epic poems created by a single poet, and the greatest epic of Persian-speaking countries. Ferdowsi is celebrated as one of the most influential figures of Persian literature and one of the greatest in the history of literature.

Except for his kunya (ابوالقاسم – Abul-Qâsem, meaning 'father of Qasem') and his pen name (فِردَوسی – Ferdowsī, meaning 'paradisic'), nothing is known with any certainty about his full name. According to Djalal Khaleghi-Motlagh, the information given by the 13th-century author Bundari about Ferdowsi's name should be taken as the most reliable. Bundari calls the poet al-Amir al-Hakim Abu'l-Qasem Mansur ibn al-Hasan al-Ferdowsi al-Tusi. From an early period on, he has been referred to by different additional names and titles, the most common one being حکیم / Hakīm ("philosopher"). Based on this, his full name is given in Persian sources as حکیم ابوالقاسم فردوسی توسی / Hakīm Abol-Qâsem Ferdowsī Tusī. Due to the non-standardised transliteration from Persian into English, different spellings of his name are used in English works, including Firdawsi, Firdusi, Firdosi, Firdausi, etc. The Encyclopaedia of Islam uses the spelling Firdawsī, based on the standardised transliteration method of the German Oriental Society. The Encyclopædia Iranica, which uses a modified version of the same method (with a stronger emphasis on modern Persian intonations), gives the spelling Ferdowsī. The modern Tajik transliteration of his name in Tajik Cyrillic is Ҳаким Абулқосим Фирдавсӣ Тӯсӣ (Hakim Abdulqosim Firdavsí Tŭsí).

Ferdowsi was born into a family of Persian landowners (dehqans) in 940 in the village of Paj, near the city of Tus, in the Khorasan region of the Samanid Empire, which is located in the present-day Razavi Khorasan province of northeastern Iran. Little is known about Ferdowsi's early life. The poet had a wife, who was probably literate and came from the same dehqan class. The dehqans were landowning Iranian aristocrats who had flourished under the Sasanian dynasty (the last pre-Islamic dynasty to rule Iran) and whose power, though diminished, had survived into the Islamic era which followed the Islamic conquests of the 7th century. The dehqans were attached to the pre-Islamic literary heritage, as their status was associated with it (so much so that dehqan is sometimes used as a synonym for "Iranian" in the Shahnameh). Thus they saw it as their task to preserve the pre-Islamic cultural traditions, including tales of legendary kings.

He had a son, who died at the age of 37, and was mourned by the poet in an elegy which he inserted into the Shahnameh.

The Islamic conquests of the 7th century brought gradual linguistic and cultural changes to the Iranian Plateau. By the late 9th century, as the power of the caliphate had weakened, several local dynasties emerged in Greater Iran. Ferdowsi grew up in Tus, a city under the control of one of these dynasties, the Samanids, who claimed descent from the Sassanid general Bahram Chobin (whose story Ferdowsi recounts in one of the later sections of the Shahnameh). The Samanid bureaucracy used the New Persian language, which had been used to bring Islam to the Eastern regions of the Iranian world and supplanted local languages, and commissioned translations of Pahlavi texts into New Persian. Abu Mansur Muhammad, a dehqan and governor of Tus, had ordered his minister Abu Mansur Mamari to invite several local scholars to compile a prose Shahnameh ("Book of Kings"), which was completed in 1010. Although it no longer survives, Ferdowsi used it as one of the sources of his epic. Samanid rulers were patrons of such important Persian poets as Rudaki and Daqiqi, and Ferdowsi followed in the footsteps of these writers.

Details about Ferdowsi's education are lacking. While it is likely that he learned Arabic in school, there is no evidence in the Shahnameh that he knew either Arabic or Pahlavi.

Ferdowsi was a Shiite Muslim, although varying views exist on what Shiite sect he belonged to. Khaleghi-Motlagh, following Theodor Nöldeke, notes that Ferdowsi displays a contradictory attitude towards religion in the Shahnameh: on the one hand, he shows a "lenient" attitude towards religion, but on the other hand, he believed that his sect was the "only true Islamic one." Khaleghi-Motlagh concurs with Nöldeke that Ferdowsi was "above all a deist and monotheist who at the same time kept faith with his forbears." Ferdowsi criticized philosophers and those who tried to prove the existence of God. He saw God's creation as the only evidence of His existence and believed everything in life to be the product of God's will. Khaleghi-Motlagh and others have suggested that a certain fatalism in Ferdowsi's work contradicts his "absolute faith in the unicity and might of God," and that this may have been the legacy of the Zurvanism of the Sasanian period.

It is possible that Ferdowsi wrote some early poems which have not survived. He began work on the Shahnameh around 977, intending it as a continuation of the work of his fellow poet Daqiqi, who had been assassinated by his slave. Like Daqiqi, Ferdowsi employed the prose Shahnameh of Abd-al-Razzaq as a source. He received generous patronage from the Samanid prince Mansur and completed the first version of the Shahnameh in 994. When the Turkic Ghaznavids overthrew the Samanids in the late 990s, Ferdowsi continued to work on the poem, rewriting sections to praise the Ghaznavid Sultan Mahmud. Mahmud's attitude to Ferdowsi and how well he rewarded the poet are matters which have long been subject to dispute and have formed the basis of legends about the poet and his patron (see below). The Turkic Mahmud may have been less interested in tales from Iranian history than the Samanids. The later sections of the Shahnameh have passages which reveal Ferdowsi's fluctuating moods: in some he complains about old age, poverty, illness and the death of his son; in others, he appears happier. Ferdowsi finally completed his epic on 8 March 1010. Virtually nothing is known with any certainty about the last decade of his life.