Russia is waging a brutal war against Ukraine. Is Russia today the same as the Soviet Union? Was the Soviet Union socialist when it collapsed in 1991? Here are basic answers.
1) 1917 until the mid-1950s: the earth-shaking Russian Revolution creates a socialist Soviet Union.
In October 1917 in Russia—a huge country that extends over parts of Europe and Asia—V.I. Lenin and the Bolshevik party (an early name for the communist party) led a mass revolution of workers, peasants, and people from broad sections of society. It overthrew the oppressive Russian empire. This ushered in the first attempt in modern history to create a society aiming to get rid of exploitation and oppression.

Lenin speaks to Red Army at Sverdlov Square, Soviet Union, May 5, 1920. (colorized)
The Russian Revolution forged a new state power. Under the leadership of Lenin and then Joseph Stalin, this new state power acted to defend and advance the revolution—in the face of hostile capitalist and imperialist powers who never stopped trying to strangle it. It waged society-wide struggle against the oppression of women. The revolution established the world's first multinational state based on equality of nations, cultures, and languages. The new state became a voluntary Union of Soviet Socialist Republics (including Ukraine)—or the Soviet Union, for short.1 The revolution created the world's first socialist economy. No longer was there private capitalist ownership and exploitation for profit. Economic development was consciously planned. From its beginnings through the early 1930s, the socialist Soviet Union gave great support to revolutionary struggles around the world. See here for more of this history.
In 1941, the Soviet Union was invaded by the German (NAZI) imperialists. Twenty-six million Soviet citizens were killed. The Soviet Union came out of World War 2 in 1945 victorious. But in many ways, how this war was fought ran counter to the goals and methods of socialism. See here for more on this.

Soviet soldiers during World War 2 battle at Stalingrad, 1942.
2) Mid-1950s until 1991: the Soviet Union continues to call itself socialist but was actually capitalist-imperialist.
In the mid-1950s, after the death of Stalin, a new bourgeois class came to power. Its main center of strength and influence was within the “communist” party and “socialist” state—which, following Stalin's death, were no longer communist or socialist despite their names. The new bourgeois rulers transformed the Soviet Union into a state capitalist society. This means that the factories, banks, etc., remained owned by the government—but now profit was guiding production. The new capitalist rulers of the Soviet Union maintained the façade of "phony socialism," as they mounted an imperialist challenge to U.S. and Western imperialism.
3) 1991: the capitalist-imperialist Soviet Union collapses and dissolves

The fall of the Berlin Wall in 1989 was one of the defining events preceding the collapse of the Soviet Union. East and West Germans stand on the Berlin Wall days before it is torn down. Credit: Wikipedia
In 1991 the “phony socialist” Soviet Union collapsed. Republics like Ukraine and Uzbekistan that had been part of the Soviet Union broke away and became independent states. Russia, the largest republic, drops the pretense and cover of socialism and becomes openly capitalist-imperialist. Factories, technology, and land were grabbed up by or sold off to wealthy private investors (many of whom had been part of the former “phony socialist” system). Oil and natural gas are controlled by the Russian government. These state energy companies operate according to an international strategy of profit-making, competing for markets with Western energy companies, and pursuing geopolitical influence in Western Europe and the Third World.
Russia has the world's fourth largest military budget; it is the world's second largest exporter of weapons (after the U.S.); and Russia has military bases in several of the republics of the former Soviet Union (like Tajikistan)and also in Syria. Russia and the U.S. together own and control 90 percent of the world's nuclear weapons.
In short, the Russia led by Vladimir Putin is a capitalist-imperialist power like the United States—but with its own particular history and features. Russia is contending with the U.S. globally, trying to create a rival pole of power in Europe, central Asia, and the Middle East. This rivalry is now focused in Ukraine... in a world in which U.S. capitalism-imperialism is still the biggest, most monstrous oppressor and exploiter on the planet.