A weak leader who should never have become a tsar. During his reign, he blindly ignored growing social tensions in Russia and other alarming trends. He was not very bright and lacked the proper education that would prepare him to lead the country. He had no interest in politics and statesmanship. He was the wrong person in the wrong position.
His worst decision was to defer to the opinion of his hawkish generals and sign the mobilisation decree in 1914. Without any good reason, Nicholas II allowed them to start a war against his cousin, the German Kaiser Wilhelm II who never intended to attack Russia. The aftermath of the war was disastrous by all measures for the monarchy, for the Russian nation, and for the tsar's family, too.
Vladimir Ilyitch Ulyanov a.k.a. Lenin
Lenin was certainly a highly intelligent man with superb managerial skills. He was well educated and travelled, too. Yet he spent all of his life in the mental prison of Marxism. Lenin lived in the times when it was already obvious that Marx's economic analysis was wrong: conditions of living of the working class is the most developed states were improving, while Marx had predicted worsening.
Lenin put all his efforts into mending the Marxist theory and implementing it. The final balance of Marxism-Leninism counted dozens of millions of dead and a bankrupt economy on the top of that.
Joseph Vissarionovich Dzhugashvili a.k.a. Stalin
Contrary to the popular belief, Stalin didn't invent GULAGs; it was Lenin. Stalin, however, perfected the idea. He also engineered the Ukrainian famine in the early 1930's; that's why the people of Ukraine welcomed Hitler as a liberator ten years later.
The main trait of Stalin's character was a strong paranoia, which included even his closest collaborators. The paranoia went as far as to killing most of the senior staff of the Red Army; 81 of the 103 generals and admirals were executed.
Oddly enough, Stalin was unsuspecting of Hitler's plans to invade the Soviet Union until it really happened. Although he received one hundred or more separate warnings of a Nazi assault, he either ignored them or, worse yet, he executed the informer. “So complete was Stalin's goodwill that full trains loaded with Soviet goods were entering Nazi-held territory even as the German assault began,” writes Daniel Pipes.
The Russian nation had hardly any worse enemy than Stalin throughout its history.
Nikita Sergeyevich Khrushchev
Khrushchev was a relief after Stalin's long reign of terror. He was a Communist, of course, but at least a sane person. Although he also assisted in Stalin's purges, he apparently didn't enjoy it. When he came to power, he introduced a more liberal regime (more liberal by Soviet standards, of course.) For instance, he abolished the special tribunals (known as troikas) operated by security agencies. He also refused Mao Zedong's proposal to start the World War III to destroy capitalism. Khrushchev preferred peaceful coexistence.
Nevertheless, Khrushchev was naïve enough to have increased aid to China, including sensitive military know-how. This was later described by historian William Kirby as “the greatest transfer of technology in world history”. The Soviet Union spent 7% of its national income between 1954 and 1959 on aid to China. For what purpose? Stalin's myopic support of Germany comes to mind.
Leonid Ilyich Brezhnev
If Khrushchev had the reputation of not being exactly an egghead, Brezhnev was outright obtuse. During his long reign (1964-1982) the Soviet Union was losing ground in science, technology, military, living standards, culture, everything. The word “Russian” became synonymous to “backward, retard, unintelligent” in the East European countries that were subjugated to the Soviet rule.
By the time of Brezhnev's death, the Soviet Union was merely a shadow of a superpower. It was holding together just by inertia.
The names of the two short-lived successors of Brezhnev are not even worthwhile to be mentioned in full. Andropov was the head of the KGB – the Soviet intelligence – and yet he was not intelligent enough to see the sorry shape the USSR was in. Perhaps he knew it, but it was way beyond his power to do anything about it. Chernenko was totally unfit for the job.
Mikhail Sergeyevich Gorbachev
From the Western point of view, Gorbachev is no doubt a hero and a champion of democracy. The irony is that he never intended to do away with socialism and to dismantle the Soviet empire.
The empire was already ripe for a collapse when Gorbachev came to power. That's why he's been consistently ranked the most unpopular leader of the past century by the Russian public. The collapse was not his fault. Yet he is ranked worse than Lenin and even Stalin.
Boris Nikolayevich Yeltsin
Another unpopular person among the Russian public. During his reign, the empire definitely crumbled, which included the emergence of post-Soviet sovereign states, hyperinflation, murky privatisation and the arrival of oligarchs, organised crime, and finally the bankruptcy of Russia in 1998. Not a pretty balance.
Vladimir Vladimirovich Putin
It's too early to evaluate Putin. For sure, he is not the worst Kremlin leader ever. When compared to his predecessor over the last century, he may be even considered as the best one. Most Russians actually think so.
History only will decide. Let's wait. In fifty-years time or so we'll be wiser.