Muhammad Ahmad bin Abd Allah (; 12 August 1844 – 22 June 1885) was a Nubian Sufi religious leader of the Samaniyya order in Sudan who, as a youth, studied Sunni Islam. In 1881, he claimed to be the Mahdi. He led a successful war against Ottoman-Egyptian military rule in Sudan and achieved a remarkable victory over the British, in the Siege of Khartoum. He created a vast Islamic state extending from the Red Sea to Central Africa, and founded a movement that remained influential in Sudan a century later.