Rukn al-Din Abu'l-Muzaffar Berkyaruq ibn Malikshah (; 1079/80 – 1105), better known as Berkyaruq (), was the fifth sultan of the Seljuk Empire from 1094 to 1105. The son and successor of Malik-Shah I (), he reigned during the opening stages of the decline and fragmentation of the empire, which marked the rise of Turkoman atabegates and principalities, which would eventually stretch from Kirman to Anatolia and Syria. His reign was marked by internal strife, mainly against other Seljuk princes. By his death in 1105, his authority had largely vanished. His infant son Malik-Shah II briefly succeeded him, until he was killed by Berkyaruq's half-brother and rival Muhammad I Tapar (). Name Berkyaruq is a Turkic word meaning "firm, unwavering light". Contrary to their Ghaznavid predecessors—who had largely abandoned their Turkic heritage in favour of Persian—the Seljuks (albeit likewise Persianized) maintained and took pride in their origins, carrying Turkic names such as Berkyaruq, Arslan Arghu or Sanjar. Background Born in 1079 or 1080 in the Seljuk capital of Isfahan, Berkyaruq was the oldest son of Malik-Shah I () and the latter's cousin, the Seljuk princess Zubayda Khatun. Berkyaruq was only thirteen at the time of his father's death in November 1092, meaning that there were no princes of age to inherit the vast Seljuk empire. Berkyaruq's half-brother Muhammad Tapar was eleven, while another half-brother named Mahmud was four. A brother of Malik-Shah titled Tutush I, who ruled Syria on his brother's behalf, claimed the throne as the only adult, but gained little support from the Turkic elite. Malik-Shah's death thus marks the start of the decline and fragmentation of the empire, with amirs and palace elites trying each to gain power by supporting one of his young sons as sultan. This would ultimately mark the start of Turkoman atabegates and principalities, which would later stretch from Kirman to Anatolia and Syria. One of Malik-Shah's wives, Terken Khatun, in cooperation with the Seljuk vizier Taj al-Mulk, installed her four-year-old son Mahmud on the throne at Baghdad. She convinced the Abbasid caliph al-Mustazhir () to have the khutba (friday sermon) read in Mahmud's name, and sent an army under the amir Qiwam al-Dawla Kirbuqa to take Isfahan and capture Berkyaruq. Meanwhile, the family and supporters of the deceased Seljuk vizier Nizam al-Mulk (known as the "Nizamiyya"), led by the Turkic slave-soldier (ghulam) Er-Ghush, supported Berkyaruq. They had Berkyaruq smuggled out of Isfahan