Mubarak is a former Egyptian military and political leader who served as the fourth President of Egypt from 1981 to 2011. Before he entered politics, Mubarak was a career officer in the Egyptian Air Force. He served as its commander from 1972 to 1975 and rose to the rank of air chief marshal in 1973. Some time in the 1950s, he returned to the Air Force Academy as an instructor, remaining there until early 1959. He was appointed Vice-President of Egypt by President Anwar Sadat in 1975 and assumed the presidency on 14 October 1981, eight days after Sadat's assassination. Mubarak's presidency lasted almost thirty years, making him Egypt's longest-serving ruler since Muhammad Ali Pasha, who ruled the country from 1805 to 1848, a reign of 43 years. Mubarak stepped down after 18 days of demonstrations during the Egyptian Revolution of 2011. On 11 February 2011, Vice President Omar Suleiman announced that Mubarak had resigned as president and transferred authority to the Supreme Council of the Armed Forces. On 13 April 2011, a prosecutor ordered Mubarak and both of his sons (Alaa and Gamal) to be detained for 15 days of questioning about allegations of corruption and abuse of power. Mubarak was then ordered to stand trial on charges of negligence for failing to halt the killing of peaceful protesters during the revolution. These trials began on 3 August 2011. On 2 June 2012, an Egyptian court sentenced Mubarak to life imprisonment. After sentencing, he was reported to have suffered a series of health crises. On 13 January 2013, Egypt's Court of Cassation (the nation's high court of appeal) overturned Mubarak's sentence and ordered a retrial. On retrial, Mubarak and his sons were convicted on 9 May 2015 of corruption and given prison sentences. Mubarak is detained in a military hospital and his sons were freed 12 October 2015 by a Cairo court.