Persian ruler of the Qājār dynasty whose incompetence precipitated a constitutional revolution in 1906.

The son of the Qājār ruler Naṣer od-Dīn Shāh, Moẓaffar od-Dīn was named crown prince and sent as governor to the northern province of Azerbaijan in 1861. He spent his 35 years as crown prince in the pursuit of pleasure; his relations with his father were frequently strained, and he was not consulted in important matters of state. Thus, when he ascended the throne in May 1896, he was unprepared for the burdens of office. At Moẓaffar's accession Iran faced a financial crisis, with annual governmental expenditures far in excess of revenues. He had to make up this deficit by contracting unpopular loans from Russia, which exacted political concessions in return.

Increased influence of Russia and Moẓaffar's squandering of the loans on extravagant European trips in 1900, 1902, and 1905 raised strong domestic opposition. The shah's capricious rule, his court's corruption, and his inability to come to grips with Iran's financial crisis brought demands for constitutional limits to his rule. Widespread popular disturbances in 1906 forced him to convene a Majles (National Consultative Assembly) that October and to grant two months later, in December, a constitution modeled on that of Belgium. The political crisis may have precipitated the heart attack from which Moẓaffar died.