Mikhail Khodorkovsky - former Yukos oil company CEO, widely assumed to be Russia's wealthiest tycoon by far.
At barely 40, he is credited with a personal fortune of $8bn - equivalent to the annual economic output of Iceland.
Mr Khodorkovsky began his career as a loyal Soviet-era Communist Party member. In 1987 - four years before the fall of the USSR - he founded what would become Menatep bank, in which he still has a large stake.
The Moscow native made his first millions in the early 1990s, when the bank acquired massive amounts of shares in companies that were privatised for bargain prices.
Mr Khodorkovsky bought Yukos at a state auction in 1995 at the knockdown price of $350m. He is thought to control 44% of the company's shares.
He was one of the first Russian tycoons to openly declare his fortune and took 26th place in Forbes magazine's list of 476 billionaires published in 2003.
Mr Khodorkovsky became a veritable example to the West, paying out dividends and running the most modern and transparent company in Russia. To get some idea of the company he used to keep, on the board of his charitable Open Russia foundation are names such as Kissinger and Rothschild.
But Mr Khodorkovsky, while he was being lionised in the West, was operating on various levels that apparently enraged those in the Kremlin who surround President Putin. Khodorkovsky was also supporting two political parties in opposition to Mr Putin, Yabloko and the Union of Rightist Forces (SPS); he has dared to say that the Russian Duma would be better off if two-thirds were independent of the Kremlin group.
Mr Khodorkovsky has been taken in for questioning twice in recent months in connection with allegations of fraud and tax evasion. The investigation began in July with the arrest of Platon Lebedev, a top Yukos shareholder, on charges of theft of state property during the 1994 privatisation of a fertiliser plant. That arrest was seen as a clear warning to Mr Khodorkovsky not to meddle in the December 2003 parliamentary elections.
Mr Khodorkovsky insisted that Yukos did not back any political group. However he has made no secret that he supports the liberal opposition to President Putin.
In September 2003 he acquired the rights to publish the prestigious Moskovskiye Novosti newspaper, and hired a leading investigative journalist and Putin critic as editor.
But analysts say it is Mr Khodorkovsky's political activism, not his wealth, that seems to attracted the Kremlin's ire.
On October 25, 2003, Mikhail Khodorkovsky was arrested at a Siberian airport by agents of the security police (FSB). Mr Khodorkovsky was flown back to Moscow for questioning and charged with several offences, including tax evasion and defrauding the state out of $1bn. The same day a Moscow court has ordered the head of Yukos to be kept in prison.
Nine days later, on November 3, 2003, Mikhail Khodorkovsky has resigned as chief executive of Yukos. In a statement, he said his aim for the next few years had been to build Yukos into an international energy company.
"But the situation as it stands today compels me to give up plans for further personal participation in developing the YukosSibneft company," he said.
"As the leader of this company, I must do my utmost to lead our working team out from under the attack which has been directed against me and my partners."
Mr Khodorkovsky, currently awaiting trial in Moscow's Matrosskaya Tishina jail, said he planned to concentrate on charity work for the Open Russia Foundation - a body he founded to promote a transparent and democratic society in Russia.
"Wherever I work, I will dedicate all my energy to my country, Russia, in whose great future I firmly believe," he said.