Five key events in post-Soviet Russia

Vladimir Putin on Monday begins his fourth term as Russian president, but has kept the possible reshuffle of his inner circle a closely guarded secret.

Here are key events in the history of post-Soviet Russia, a history in which Putin has played a leading role.

Death of the USSR

On December 8, 1991, Boris Yeltsin, who has served six months as president of the Russian Federation, stands alongside the leaders of Ukraine and Belarus and proclaims the death of the Union of Soviet Socialist Republics (USSR), commonly known as the Soviet Union.

The leaders of several former republics, including Russia, agree that the Soviet Union "no longer exists". Soon afterwards Soviet leader Mikhail Gorbachev has no option but to resign.

Yeltsin swiftly launches an ambitious programme of market reforms, privatising key sectors, easing price controls, allowing the ruble to float.

In 1993, he dissolves Russian parliament unconstitutionally, triggering a rebellion, then orders tanks to shell parliament building where deputies have taken refuge. 148 are killed according to the official toll.

The following year Yeltsin sends Russian troops into the small independent republic of Chechnya. In 1996 a peace deal ends the first Chechen war which left tens of thousands dead.

The 1998 financial crisis plunges millions of Russians into poverty. The health and education systems crumble and corruption spreads.

A tsar is born

In August 1999, Yeltsin propelled a virtually unknown figure to become his prime minister. That man was Vladimir Putin who had been head of the KGB's successor, the FSB intelligence service.

Putin swiftly forged an image as a strongman in a country traumatised by a series of attacks attributed to Chechen separatists.

Yeltsin, battling health and drinking problems, sensationally resigned on New Year's Eve 1999, leaving his protege to take control of the biggest country on Earth.

Putin formally succeeded Yeltsin as president at the ensuing election in March 2000.

From 2000 to 2009 the conflict in Chechnya left tens of millions dead.

During his first two mandates -- he was re-elected in 2004 -- Putin reinforced his control over parliament, placed regional governors firmly under Moscow's thumb, demanded unconditional loyalty from the media and restored all the powers of the intelligence service.

He also took on Russia's new super-rich oligarchs, who prospered under Yeltsin, including oil tycoon Mikhail Khodorkovsky who was imprisoned for ten years and now lives in London.

Meanwhile Putin also addressed Russia's economic woes, introducing strict monetary controls but also benefiting from huge oil revenues.

President Medvedev

As Russia's constitution ruled out a third consecutive mandate, Putin names a young ally, deputy prime minister Dmitry Medvedev, as his preferred successor as president.

Medvedev is duly elected in March 2008, with no real opposition standing against him.

Putin becomes prime minister and takes the reins of the ruling United Russia party, which controls parliament.

In 2009 Russia is hit hard by the global economic crisis, but afterwards growth resumes.

Controversial return to the top job

In December 2011 a protest movement begins -- unprecedented since Putin came to power -- angered by what the opposition denounced as fraudulent elections won by Putin's United Russia party.

However the wave of protests does not prevent Putin from returning to the presidency in 2012, for a six-year mandate thanks to a constitutional reform.

His election, with 64 percent of the vote, had "serious problems" according to the Organization for Security and Co-operation in Europe (OSCE) which complained that there had been no serious competition to Putin and the result was never in doubt.".

Reviving 'Great Russia'

Putin seeks to restore "Great Russia" , annexing the Ukrainian peninsula of Crimea in 2014.

This move brings Russia's relations with the West to their lowest levels since the Cold War, with Western powers accusing Moscow of also militarily supporting a separatist struggle in eastern Ukraine, a charge the Kremlin denies.

The United States and European nations impose a raft of sanctions which hit the Russian economy.

Russia becomes a major player in the Syrian conflict, intervening in September 2015 and helping the forces of President Bashar al-Assad to get the better of the rebels.