By James Rodgers
BBC News, Moscow
The greatest riddle at the heart of contemporary Russian power has been solved.
Dmitry Medvedev is one of the youngest politicians in the Kremlin
President Vladimir Putin has named Dmitry Medvedev as his chosen successor.
Mr Putin's support puts Mr Medvedev in the strongest possible position ahead of March's presidential election.
Mr Putin's popularity means that that whoever he nominates is likely to win.
The announcement brings to an end years of speculation about who might come next.
Mr Medvedev has long been listed among the possible front-runners.
The choice of a young, energetic candidate - Mr Medvedev is 42 - is also likely to dampen suggestions that Mr Putin was somehow planning to stay in power.
No KGB background
Mr Medvedev is one of the circle of powerful people in Russia today who began their careers in St Petersburg.
He is a long-term ally of Mr Putin. He ran Mr Putin's election campaign for his first term as president in 2000.
Mr Putin referred to this long working relationship during a televised meeting with political leaders to announce the decision to endorse Mr Medvedev's candidacy.
Mr Putin's endorsement could be decisive in presidential elections
"I have known him very closely for more than 17 years and I completely and fully support this proposal," Mr Putin said.
Mr Medvedev is seen as being on the liberal wing of the current administration.
He is not one of the Kremlin figures with a KGB background. The fact that he is not one of the more hawkish figures previously linked with a future presidential bid is likely to be privately welcomed by Western governments.
He has combined his current post of first deputy prime minister with the chairmanship of the Russian gas giant, Gazprom.
Mr Medvedev's most prominent role in recent months has been as the man responsible for Russia's "national projects".
These are schemes designed to spend some of the country's new wealth on improving healthcare, housing, agriculture, and the arts.
This may have provided the launch-pad for his presidential ambitions.
"National projects have been hugely successful for him," says Yaroslav Lissovolik, chief economist at Deutsche Bank in Moscow.
"He passed Putin's test."
Mr Medvedev has strong business connections, like Gazprom
Mr Lissovolik describes Mr Medvedev as the most liberal of the possible candidates - both economically and politically.
He predicts that under a Medvedev presidency Russia would integrate further into the world economy.
The announcement appears to have solved one riddle, and focused attention very sharply on another: what are Mr Putin's plans?
United Russia's recent, resounding victory in parliamentary elections has confirmed Vladimir Putin as Russia's most popular politician.
The electorate here has largely brushed aside the verdict of Western observers that the poll was not fair.
All eyes will be on Mr Putin's next move - trying to work out what his public role will be, and how much real influence it will carry.
Mr Medvedev can probably expect to be put under pressure from others who saw themselves as a possible president.
Some analysts say a Medvedev presidency is not inevitable.
"It's too early to say Medvedev is the next president - naming him saves enough time for potential other options to appear - so Medvedev could let himself down and someone else would take over," cautions Nikolai Petrov of the Moscow Carnegie Centre.
"That could be both before and after the presidential elections, if he carries out unpopular reforms."