Short answers, pulled from the story.
Leonid Brezhnev served as General Secretary of the Communist Party of the Soviet Union from 1964 until his death on the 10th of November 1982, a tenure second in length only to Joseph Stalin's. He also held the office of Chairman of the Presidium of the Supreme Soviet from 1960 to 1964 and again from 1977 to 1982.
The Brezhnev Doctrine was the principle, announced following the Soviet suppression of Czechoslovakia's Prague Spring in 1968, that any threat to socialist rule in a Soviet Bloc state was a threat to all and would justify military intervention. Brezhnev formally articulated it at the Fifth Congress of the Polish United Workers' Party on the 13th of November 1968. Soviet leader Mikhail Gorbachev repudiated the doctrine in the late 1980s.
The Era of Stagnation is a term coined by Mikhail Gorbachev to describe the period of socioeconomic decline during Brezhnev's rule. The CIA estimated the Soviet economy peaked in the early 1970s, after which GNP growth fell to between 1% and 2% per year. The decline was driven by the prioritization of heavy industry and military spending over consumer goods, the absence of meaningful economic reform, and widespread corruption.
Brezhnev and U.S. President Richard Nixon signed the SALT I Treaty at the 1972 Moscow Summit. The treaty set limits on each side's nuclear missiles and included the Anti-Ballistic Missile Treaty, which banned both countries from building systems to intercept incoming missiles. The agreement gave the Soviet Union nuclear parity with the United States for the first time in the Cold War.
Brezhnev died on the 10th of November 1982 from a heart attack, three days after his final public appearance at the 65th anniversary of the October Revolution. He was succeeded as General Secretary by Yuri Andropov. Brezhnev was buried in his Marshal's uniform in the Kremlin Wall Necropolis in Red Square.
Brezhnev has received consistently high approval ratings in post-Soviet Russian polls. In a 2013 Levada Center poll he received 56% approval, ranking above both Vladimir Lenin and Joseph Stalin as Russians' favourite 20th-century leader. A 2007 VTsIOM survey found the majority of Russians would prefer to have lived during the Brezhnev era over any other period of 20th-century Soviet history.