Nusrat al-Din Abu Bakr (Persian: نصرت الدین ابوبکر), was the ruler (atabeg) of the Eldiguzids from 1191 to 1210. He used the titles of Jahan-pahlavan ("champion of the world"), al-Malik al-Mu'azzam ("the respected king"), and Shahanshah al-A'zam ("the great king of kings").