Muhammad Hosni El Sayed Mubarak (born 4 May 1928) is a former Egyptian President, leader and military commander. He served as the fourth President of Egypt from 1981 to 2011. Mubarak was appointed Vice President of Egypt in 1975 and assumed the presidency on 14 October 1981, following the assassination of President Anwar Sadat. His almost thirty-year presidency made him Egypt's longest-serving ruler since Muhammad Ali Pasha. Before he entered politics, Mubarak was a career officer in the Egyptian Air Force, serving as its commander from 1972 to 1975 and rising to the rank of air chief marshal. Mubarak stepped down after 18 days of demonstrations during the 2011 Egyptian revolution when, 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, a prosecutor ordered Mubarak and both of his sons to be detained for 15 days of questioning about allegations of corruption and abuse of power. He was then ordered to stand trial on charges of negligence for not giving orders to stop the killing of peaceful protestors during the revolution. These trials officially began on 3 August 2011. Egypt's military prosecutors then also proclaimed that they were investigating Mubarak's role in the assassination of his predecessor Anwar Sadat. On 2 June 2012, Mubarak was sentenced to life imprisonment by an Egyptian court. After sentencing, he was reported to have suffered a series of health crises. On 20 August 2013, an Egyptian court ordered Mubarak’s release, because there are no more legal grounds for his detention.