Mikhail Khodorkovsky, an opponent of Vladimir Putin, has been released from prison after he was pardoned by the president.
Mr Khodorkovsky arrived in Berlin this afternoon.
In a statement, he said that he had sought a pardon from the Russian president for family reasons and did not admit guilt.
Once Russia's richest man, the 50-year-old looked pale and thin but happy in a photograph of him being greeted by German well-wishers on the tarmac after landing on a private jet.
Within hours of being released from Penal Colony No 7 at Segezha, deep in the sub-Arctic forest near the Finnish border, Mr Khodorkovsky was in the German capital.
He said: "I appealed to the Russian president on 12 November with a request for a pardon in connection with family circumstances.
"The issue of an admission of guilt was not raised.
"I am very eager for the moment when I can hug my loved ones," he said. "I will welcome the opportunity to celebrate this upcoming holiday season with my family."
President Putin signed the decree pardoning Mr Khodorkovsky this morning.
He announced unexpectedly yesterday that he would pardon the former Yukos oil company chief.
A Russian government source said freeing Mr Khodorkovsky could deflect international complaints about Mr Putin's human rights record as Russia prepares to host the Winter Olympics at Sochi in seven weeks' time.
Mr Putin said in the decree that the decision to pardon Mr Khodorkovsky was "guided by the principles of humanity".
Mr Putin told reporters yesterday that Mr Khodorkovsky had asked for a pardon, citing his elderly mother's poor health, and that he would grant it.
Mr Khodorkovsky's mother Marina, 79, said: "I want to just hug him. I don't even know yet what I amgoing to say to him."
Her son said last month that she was facing a second bout of cancer and he might not see her again.
"My father is free and safely in Germany," his son, Pavel Khodorkovsky, said on Twitter. "Thank you all for the support you've given my family over these years!"
The former oil baron had been due to be released next August but supporters feared the sentence could be extended, as it was before.
He spent the last few years working at the jail, in an area once part of Stalin's Gulag labour camp system.
In flying to Germany and possibly into exile on a hastily issued passport, Mr Khodorkovsky, named a "prisoner of conscience" by Amnesty International, was following a route taken by Soviet-era dissidents like "Gulag Archipelago" author Alexander Solzhenitsyn, who was expelled to West Germany 40 years ago.
Mr Khodorkovsky was greeted at the airport by Hans-Dietrich Genscher, the former German foreign minister who played a major role in East-West relations at the end of the Cold War and who had helped organise the plane to bring Mr Khodorkovsky to Berlin.
The oil baron fell out with Mr Putin before his arrest in 2003 as the president clipped the wings of wealthy "oligarchs" who had become powerful during the chaotic years of Boris Yeltsin's rule following the collapse of Soviet communism.
His company, Yukos, was broken up and sold off, mainly into state hands, following his arrest at gunpoint on an airport runway in Siberia on fraud and tax evasion charges.
In the eyes of critics at home and abroad, his jailing was a significant stain on the record of Mr Putin who succeeded Yeltsin in 2000 and has not ruled out seeking another six-year term in 2018.
Mr Khodorkovsky came to represent what critics say is the Kremlin's misuse of the judicial system, curbing the rule of law, and of its refusal to permit dissent.
Mr Putin, who mounted savage personal attacks on Mr Khodorkovsky, has always insisted he got his what he deserved in the courts for theft on a grand scale.