Short answers, pulled from the story.
Vladimir Lenin created the Office of General Secretary in 1922 with a narrow mandate. The role existed to handle technical party work rather than political strategy.
Joseph Stalin remained the highest-ranked secretary for thirty years and seven months until his death on the 5th of March 1953. He became the de facto leader of the USSR by 1928 despite holding only a secretarial title.
Leonid Brezhnev succeeded Khrushchev in October 1964 but governed as part of a collective leadership arrangement. This system formed another troika with Premier Alexei Kosygin and Chairman Nikolai Podgorny.
Mikhail Gorbachev resigned from his party office following the failed August coup later that year. Vladimir Ivashko served as Acting General Secretary for only five days before Boris Yeltsin suspended all activity in the Communist Party.
Prominent Second Secretaries included Mikhail Suslov, Frol Kozlov, and Nikolai Podgorny. All post-Stalin General Secretaries began their careers as Second Secretaries.