Jalāl al-Dawla Mu'izz al-Dunyā Wa'l-Din Abu'l-Fatḥ ibn Alp Arslān (8 August 1055 – 19 November 1092, full name: Persian: معزالدنیا و الدین ملکشاه بن محمد الب ارسلان قسیم امیرالمومنین), better known by his regnal name of Malik-Shah I (Persian: ملکشاه, Turkish: Melikşah), was sultan of the Seljuk Empire from 1072 to 1092.
During his youth, he spent his time participating in the campaigns of his father Alp Arslan, along the latter's vizier Nizam al-Mulk. During one of such campaigns in 1072, Alp Arslan was fatally wounded and died only a few days later. After that, Malik-Shah was crowned as the new sultan of the empire, however, Malik-Shah did not access the throne peacefully, and had to fight his uncle Qavurt, who claimed the throne. Although Malik-Shah was the nominal head of the Seljuk state, Nizam al-Mulk held near absolute power during his reign. Malik-Shah spent the rest of his reign waging war against the Karakhanids on the eastern side, and establishing order in the Caucasus.
Malik-Shah's death to this day remains under dispute; according to some scholars, he was poisoned by Abbasid caliph al-Muqtadi, while others say that he was poisoned by the supporters of Nizam al-Mulk.