Answer
Alp Arslan, the Seljuk Sultan, played a pivotal role in defeating the Byzantine emperor Romanos IV Diogenes at the Battle of Manzikert in 1071. This significant victory marked a turning point in the balance of power between the Byzantine Empire and the Seljuk Turks, leading to the eventual decline of Byzantine control over Anatolia and opening the doors for the establishment of the Seljuk Sultanate of Rum.