The Pahlavi dynasty (Persian: خاندان پهلوی) is the last Iranian royal dynasty, ruling for almost 54 years between 1925 and 1979. The dynasty was founded by a non-aristocratic Mazanderani soldier in modern times, who took on the name of the Pahlavi language spoken in the pre-Islamic Sasanian Empire in order to strengthen his nationalist credentials.The dynasty replaced the Qajar dynasty in the early 1920s, beginning on 14 January 1921 when 41-year-old soldier Reza Khan was promoted by British General Edmund Ironside to lead the British-run Persian Cossack Brigade. About a month later, under British direction, Reza Khan's 3,000-4,000 strong detachment of the Cossack Brigade reached Tehran in what became known as the 1921 Persian coup d'état. The rest of the country was taken by 1923, and by October 1925 the Majlis agreed to depose and formally exile Ahmad Shah Qajar. The Majlis declared Reza Pahlavi as the new Shah of Iran on 12 December 1925, pursuant to the Persian Constitution of 1906. Initially, Pahlavi had planned to declare the country a republic, as his contemporary Atatürk had done in Turkey, but abandoned the idea in the face of British and clerical opposition.The dynasty ruled Iran for 28 years as a form of constitutional monarchy from 1925 until 1953, and following the overthrow of the democratically elected prime minister, for a further 26 years as a more autocratic monarchy until the dynasty was itself overthrown in 1979.