Yegor Timurovich Gaidar (/jɪˈɡɔːr ɡaɪˈdɑːr/; Russian: Егор Тимурович Гайдар, IPA: [jɪˈɡor tʲɪˈmurəvʲɪtɕ ɡɐjˈdar]; 19 March 1956 – 16 December 2009) was a Soviet and Russian economist, politician, and author who was the acting Prime Minister of Russia in 1992 and simultaneously held several other cabinet roles. Gaidar was also in the State Duma from 1993 to 1996 and from 1999 to 2003 as a member of Democratic Choice of Russia and the Union of Right Forces.

Gaidar was the son of a Soviet naval officer and graduated from Moscow State University. He worked in economic research institutes before joining a commission that advised Soviet President Mikhail Gorbachev in the 1980s. Following the dissolution of the Soviet Union, Gaidar was the chief architect of Russia's controversial shock therapy reforms, which brought him both praise and harsh criticism. He entered the cabinet led by President Boris Yeltsin as Minister of Finance, Minister of Economy, and Deputy Prime Minister for Economic Policy, serving from 1991 to 1992. He was also the First Deputy Prime Minister of Russia in 1992, with Yeltsin and later himself as acting prime minister, and again from 1993 to 1994, in Viktor Chernomyrdin's cabinet, where he was also the acting Minister of Economy. Gaidar became widely unpopular for his reforms to transition Russia to a market economy, during which the country experienced hyperinflation and mass impoverishment, and the parliament pressured Yeltsin to remove him. He left the government in early 1994, when the administration decided to take a more gradual approach to economic reform.

Many Russians held him responsible for the economic hardships that plagued the Russian Federation in the 1990s, although liberals praised him as a man who did what had to be done to save the country from complete collapse. Gaidar founded the party Democratic Choice of Russia, and as a member of that party was elected to the State Duma in the 1993 legislative election. He stopped supporting Boris Yeltsin due to the First Chechen War. Democratic Choice of Russia failed to win any seats in the 1995 election, but Gaidar returned to the Duma in the 1999 election when his party joined the Union of Right Forces electoral bloc. He was an advisor to Mikhail Kasyanov, the prime minister in the early administration of President Vladimir Putin. After the electoral bloc failed to keep its seats in the 2003 election, Gaidar left politics and returned to academic work, though he was still consulted for economic advice. He went on to publish several books on economics. Gaidar died of pulmonary edema provoked by myocardial ischemia in 2009.

Gaidar was born in 1956 in Moscow, RSFSR, Soviet Union, the son of Ariadna Bazhova and Pravda military correspondent Timur Gaidar, who fought in the Bay of Pigs Invasion and was a friend of Raúl Castro. His paternal grandfather was Soviet writer Arkady Gaidar and his maternal grandfather was writer Pavel Bazhov. They had both been devoted Bolsheviks that fought in the 1917 Russian Revolution. Despite the Turkic-sounding surname, Gaidar was Russian; his grandfather, originally called "Golikov", adopted the name "Gaidar" from the Khakas language as a nom-de-plume.

Because his father was a Soviet Navy one-star admiral and was often posted to "hot spots," it has been speculated that he was a member of the GRU, Soviet military intelligence. Yegor Gaidar spent part of his childhood at his father's postings. He was in Cuba during the Cuban Missile Crisis in 1962, and was in Yugoslavia in 1966, where, as he later said, he saw a socialist country with a market economy, open political discourse, and fully stocked shops. His father noticed that he had a talent for mathematics and entrusted him with keeping business expenditure reports, which was the start of his interest in economics. According to Gaidar, the Soviet reaction to the 1968 Prague Spring, along with the turn of Yugoslavia away from the Soviet model and radical economic reforms in Hungary, had an impact on his views. He later studied at Moscow State University's Faculty of Economics, where he learned about Marxist theory as well as other economic thought. One of Gaidar's professors explained to his students in private in the 1970s why he thought the Soviet economy was on the verge of collapse, and was only propped up by revenue from oil exports.

During his studies, Gaidar reached the view that any form of socialism, including market socialism, was destined to fail. Despite this, he continued to use Marxist methodology, including the Marxist explanation that the genesis of economic systems was the development of productive forces.

Gaidar graduated with honors from Moscow State University in 1980 and worked as a researcher in several academic institutes. He studied liberalizing reforms in socialist economies. After obtaining his doctorate in economics, Gaidar was put in charge of the economic policy section of the party's ideological journal, Communist. In 1990 he became the head of the economic section of Pravda. Gaidar was a member of the Communist Party of the Soviet Union until it was dissolved in August 1991.

The perestroika reforms allowed Gaidar and other young economists to publish their ideas in the party's official journals, and his position in newspapers increased his influence in party ideological circles. He supported the reforms of President Mikhail Gorbachev and became a member of the commission under the Soviet Politburo to study ways to improve the management of the economy. During this time Gaidar met Gorbachev on several occasions, and participated in the introduction to government terminology such terms as radical economic reform, market, individual entrepreneurship, unemployment, poverty, and inflation, among others. Gaidar thought that the government should focus on liberalization and financial stabilization. Gorbachev was receptive to advice from liberal economists, but he was also under pressure from traditional forces. Meanwhile, the Soviet economy was experiencing a deep crisis as oil prices declined significantly between 1981 and 1987, undermining the Soviet Union's ability to import consumer goods such as food using energy revenue. Gorbachev rejected a 500 Day Plan for reform that was proposed by some economists in favor of a less radical version, and without a timetable. Gaidar criticized the plan as being too radical, but in April 1990 he wrote that "the time is past when the economy could be stabilized without difficult and unpopular measures." In late 1990 he organized the Institute for Economic Policy.