Brezhnev assumed power in 1964. He is most closely associated with the beginning of the decline of The Soviet Union because under his rule corruption flourished.
One of the great “What Ifs”, what if Khrushchev was able to hang onto to power. For all of his bluster, he seemed to be a fairly decent guy as far as Soviet leaders go. Would he had invaded Czechoslovakia, like Brezhnev did?