Brezhnev had been the right-hand man of Nikita Khrushchev for a long time, and so when his boss was deposed by a motley mix of hardliners in 1964 (Brezhnev himself among them) he was well-positioned to take power. His early reign was a bit awkward as the government was dominated by hardliners, who had little tolerance for the 'softie' Brezhnev and his liberal-socialist sympathies. Accordingly the USSR reversed some of Khrushchev's "De-Stalinization" measures of the previous years—calling it a complete reversal, however, would be disingenuous: Brezhnev, more so than both his strong-willed predecessor, or his more open-minded successors like Mikhail Gorbachev, championed the idea of collective leadership, a direct rejection of the concentration of power that had happened under Josef Stalin up and during the Second World War.
Brezhnev, and those who held similar opinions, after all were veterans of the war—they suggested that complete and total authority of government in a single individual might have a place in a war where literally tens of millions of your countrymen are being exterminated, or simply by an unavoidable consequence if it were not already in place, but it did not have a place in a "Cold War", both from contemporaneous and from Marxist-Leninist standpoints. In fact, the roles of Premier and First Secretary had been previously split during Georgy Malenkov's brief and ill-fated spell as leader, only to be re-combined a few years into Khrushchev's regime. As such, while concentrating considerable power in his own office (most broadly, the General Secretary of the Communist Party, as Stalin had been), he strongly advocated a formal and practical distribution of powers across offices, not unlike that of Yugoslavia's Tito—this gave power to some of the country's most effective leaders, like Soviet Prime Minister Alexey Kosygin, Foreign Minister Andrey Gromyko, and President Nikolay Podgorny.
On the other hand, Brezhnev's government did roll back some of the nuanced economic liberalism of Khrushchev, while simultaneously undoing the informal ban on "all things Stalin"—a move that might potentially cast him in a more positive light versus the prior decade's political rejection, but did open up the possibility of blaming some of Stalin's contemporaries, who bore at least some real responsibility, for the most grievous acts of the early decades (so long as it did not cast the current government in a negative light). Another rollback of Khrushchev's policies was the formal return of political power along lines of national delimitation, particularly along ethnic minority lines, wherein Khrushchev's government had concentrated said power in the hands of Moscow. The move towards conventional military investment was done so it wouldn't be forced to use tactical nuclear weapons in the event of an armed conflict as per Khrushchevian doctrine.
When the Prague Spring arose in 1968 Brezhnev was intensely sympathetic to their cause and spent months talking with his friends in the Czechoslovakian leadership, trying to work out a peaceable solution in which a prospective Socialist Democracy could co-exist with Communist Dictatorships 'and' remain in the Warsaw Pact. Ultimately the Czechoslovaks had taken it 'too far' in the eyes of virtually the entire Soviet leadership by autumn and, to strengthen Brezhnev's resolve, head of the KGB Yuri Andropov fabricated reports that the country was on the verge of leaving the Warsaw Pact and joining NATO unless immediate action was taken. Brezhnev promptly called in Warsaw Pact forces to topple the regime, and seems not to have appreciated the deception when he learned of it.
The most important long-term consequence of this was that Soviet hardliners suddenly began singing Brezhnev's praises, seeing him as 'one of them' (an impression he encouraged). In one fell swoop he had gained the anti-capitalist credentials he needed to negotiate with capitalists without looking weak. This set the stage for the demonstrably anti-capitalist Brezhnev and his contemporary the US President Gerald Ford (an anti-communist) to negotiate Détente with one another. Brezhnev's move also made big waves within the Warsaw Pact. Although Khrushchev, another 'liberal' (by Soviet standards), had crushed the Hungarian Revolution of 1956 in much the same way, the Soviet government saw fit to formally justify the ending of the Prague Spring with what became known as the "Brezhnev doctrine". The Brezhnev doctrine stated that communist countries which started to get crazy ideas about flirting with socialism (there are big differences) or semi-democratic representative institutions or whatnot needed to be put back on course.
Brezhnev oversaw a period of stability in the Soviet Union, but also stagnation. Russians rank him as their favorite leader of the twentieth century, thinking of him as the "good old man" who presided over a golden age. Internationally, the 1970s was the period of greatest communist success in the Cold War. The communist side won The Vietnam War. Neighboring Laos and Cambodia also went communist. So did Afghanistan, Angola, Mozambique, and Benin. Meanwhile, the West was reeling from an oil crisis and the American economy was suffering from stagflation. It was a great time to be a commie!
Then (already ailing and senile) Brezhnev got the brilliant idea to invade Afghanistannote in order to put down an anti-communist rebellion there. This would prove to be the greatest (and last) test for the Brezhnev doctrine. By then, his health started to take a turn for the worst and he would die in 1982.
Brezhnev in popular culture:
- Appears in Oliver Stone's Nixon meeting the President about the SALT II treaty.
- The unnamed Soviet premier in the James Bond film Octopussy was obviously intended to be Brezhnev, who actually died before the film's premiere.
- He briefly appears at the end of The Death of Stalin, participating in the coup to remove Beria from power. In the final scene, he is in the background keenly looking in Khrushchev's direction.
- In Spitting Image Brezhnev was often used as an extra, often in scenes with Russian settings. Since the show debuted in 1984 Brezhnev himself had already been dead for two years and was never featured as himself on the show.
- He is mentioned in Pink Floyd's song "The Fletcher Memorial Home" from the album The Final Cut, as one of the "overgrown infants" and "incurable tyrants" who ought to be sent to a rest home.
- He is one of the many people with the initials "LB" in the verse of "It's the End of the World As We Know It" that named the trope Something Something Leonard Bernstein.
- He appeared in an Alternate History episode of American Dad!, in which Walter Mondale won the 1984 election and so surrendered America to the USSR after only a few weeks in office. This can be considered an anachronism, since Brezhnev died in 1982, but it can also be Hand Waved as part of the Butterfly Effect.