Reza Shah Pahlavi (previously Reza Khan ; 15 March 1878 – 26 July 1944) ( Persian : رضاشاه پهلوی ) was an Iranian military officer and monarch who was the founder of the Pahlavi dynasty and Shah of Iran from 1925 to 1941. Originally an army officer, he became a politician, serving as minister of war and prime minister of Iran , and was elected shah following the deposition of Ahmad Shah , the last monarch of the Qajar dynasty .