Muhammad I Tapar (Persian: محمد اول تاپار; 20 January 1082 – 18 April 1118), was the sultan of the Seljuk Empire from 1105 to 1118.

[2][3] He succeeded his nephew, Malik Shah II, as Seljuq Sultan in Baghdad, and thus was theoretically the head of the dynasty, although his brother Ahmad Sanjar in Khorasan held more practical power.

Muhammad I probably allied himself with Radwan of Aleppo in the battle of the Khabur River against Kilij Arslan I, the sultan of Rüm, in 1107, in which the latter was defeated and killed.

When Ahmad arrived to the court, Muhammad I appointed him as his vizier, replacing Sa'd al-Mulk Abu'l-Mahasen Abi, who had been recently executed on suspicion of heresy.

Muhammad I, along with his vizier Ahmad, later campaigned in Iraq, where they defeated and killed the Mazyadid ruler Sayf al-dawla Sadaqa ibn Mansur, who bore the title "king of the Arabs".

In 1109, Muhammad I sent Ahmad and Chavli Saqavu to capture the Ismaili fortresses of Alamut and Ostavand, but they failed to achieve any decisive result and withdrew.

According to the historian Imad ad-Din al-Isfahani (died in 1201), Muhammad was "the perfect man of the Seljuk dynasty and their strongest steed".

[24] Muhammad's ceaseless campaigns inspired one of his poets, Iranshah, to compose the Persian epic poem of Bahman-nama, an Iranian mythological story about the constant battles between Kay Bahman and Rostam's family.