Tughril Beg (tōōg´rēl bĕg), 990–1063, founder of the Seljuk Turk dynasty ruling (11th–14th cent.) parts of Anatolia, Iraq, Persia, and Syria. He was early successful in conquests with his brother, who eventually governed Khorasan. Tughril Beg conquered Persia (1040–44) and Iraq (1055). His ideology sought to reinforce unity in the Islamic world. By 1060 he had assumed control of former Buyid territory.