Abu Mohammad Moshrefoldin Mosleh ebn Abdollah ebn Mosharraf, better known by his pen name Saadi, also known as Saadi of Shiraz (سعدی شیرازی, Saʿdī Shīrāzī; born 1210; died 1291 or 1292), was an Iranian poet and prose writer of the Islamic Golden Age. He is recognized for the quality of his writings and for the depth of his social and moral thoughts.

Saadi is widely recognized as one of the greatest poets of the classical literary tradition, earning him the nickname "The Master of Speech" or "The Wordsmith" (استاد سخن ostâd-e soxan) or simply "Master" (استاد ostâd) among Persian scholars. He has been quoted in the Western traditions as well. His book, Bustan has been ranked as one of the 100 greatest books of all time by The Guardian.

Saadi was of Persian stock and his birth date is uncertain; most scholars consider him to have been born in 1209 or 1210. He was from the city of Shiraz, the provincial capital of the Fars province. Since 1148, the province had been under the rule of the Salghurids, a Persianate dynasty of Turkoman origin.

There is little certainty concerning Saadi's life. Although his own writings, particularly the Bustan and Gulistan, contain many supposedly autobiographical memories, many of these are historically unlikely and are likely made up or cast in the first person for rhetorical effect. Even the earliest references to him in external literature differ in crucial details. Even his real name is uncertain. In sources, his entire name—which consists of his given name, honorific (laqab), agnomen (kunya), and patronymic—is spelled in several differing ways.

The oldest known source to mention his full name is the Talḵiṣ al-majmaʿ al-ādāb fi moʿjam al-alqāb ("Summary of the gathering of refinements concerning the lexicon of honorifics") by Ibn al-Fuwati (died 1323). In a letter dated 1262, he asked Saadi for samples of his Arabic poetry and mentioned his full name as "Muslih al-Din Abu Muhammad Abd-Allah ibn Musharrif." The Iranian scholar Saeed Nafisi favoured this version of his full name. However, the majority of other academics favour the information found in the early manuscripts of Saadi's writings. For instance, the British Iranologist Edward Granville Browne used a text from 1328 to argue that Saadi's full name was "Musharrif al-Din ibn Muslih al-Din Abd-Allah." The majority of subsequent Western academics, including Arthur John Arberry, Jan Rypka, and R. Davis, include "Abd-Allah" in Saadi's patronymic, hence "Abu Abd-Allah Musharrif al-Din Muslih".

The Iranian scholar Zabihollah Safa came to the conclusion that "Muslih" was Saadi's given name and gives his full name as "Abu Muhammad Musharrif al-Din Muslih ibn Abd-Allah ibn Musharrif" based on the preface to one of the oldest surviving compilations of Saadi's collected works, which was created by his fellow townsman Ali ibn Ahmad ibn Abu Bakr Bisotun in 1326. In his book Nafahat al-Uns, the Persian poet Jami (died 1492) provides virtually the same version of the name. This version is also supported by the Iranologist Paul E. Losensky.

His pen name "Saadi" is unambiguous as it appears frequently in his work and acts as his signature in all of his ghazals (amatory poem or ode). However, there are doubts over where it came from. Since two members of the Salghurid dynasty named "Sa'd" ruled for most of Saadi's life, it is likely that the inspiration for the name came from his allegiance to them. The Iranian scholar Abdolhossein Zarrinkoob argues that "Sa'd" or "Banu Sa'd" was also the name of the dynasty itself, hence Saadi's adoption of the name, which demonstrated his loyalty to them.

Saadi appears to have received his early education from his father, who also instilled in him lifelong tolerance values. During Saadi's adolescence, his father died, thus leaving him an orphan. Probably around 1223/24, when Sa'd I was briefly deposed by Ghiyath al-Din Pirshah, Saadi, still a teenager, left for Baghdad to continue his education there.