Prince Hamid Reza Pahlavi in Evin Prison

In 1921 Reza Khan (later Reza Shah Pahlavi), an officer in Iran's only military force (Cossack Brigade) used his troops to support a coup against the government of Qajar Dynasty. Within four years he had established himself as the most powerful person in the country by suppressing rebellions and establishing order. In 1925 a specially convened assembly deposed Ahmad Shah, the last ruler of the Qajar dynasty, and named Reza Khan, who earlier had adopted the surname Pahlavi, as the new shah.