Sayyid Muhammad Abdullah Hassan (born 1856, Somalia, died 1920, Ogaden) was Somalia's religious and nationalist leader (called the ‘Mad Mullah’ by the British). For 20 years he led armed resistance against British, Italian, and Ethiopian colonialist forces in Somalia. He was the eldest son of Sheikh Abdille, a religious Ogaden Somali.
In 1897, fearing Christian influence he started preaching religious reform. Hassan got weapons from Turkey, Sudan, and other Muslim countries. He appointed ministers in different areas of Somalia and sent emissaries appealing for Somalis to join his movement. In 1900 Hassan attacked the Ethiopian garrison at Jijiga successfully. He then raided British areas. From 1901-1904, the Dervish army inflicted heavy losses on Ethiopian, British and Italian forces. By 1913, Hassen ruled the entire hinterland of the Somali peninsula.