What is "al-mujahid"

Al Malik Al-Mujahid Asad ad-Din Shirkuh II was the Ayyubid emir of Homs from 1186-1240. He was the son of An-Nasir Muhammad ibn Shirkuh, grandson of Shirkuh and second cousin of Saladin. His domains also included Palmyra and ar-Rahba. Al Mujahid became emir at the age of thirteen when his father died unexpectedly in Homs on 4 March 1186 (10 Dhu’l Hijja 581).