Russian metals tycoon and US basketball team owner Mikhail Prokhorov has said he intends to challenge Prime Minister Vladimir Putin in next year's presidential elections.
"I have made the most serious decision of my life. I am running for president," Mr Prokhorov told reporters.
The owner of NBA's New Jersey Nets basketball team had previously made a short-lived effort to challenge Mr Putin's United Russia party in this month's parliamentary elections. However, he resigned following an internal power struggle that he blamed on the Kremlin.
''If you remember, the Kremlin removed me and my supporters from Pravoye Delo (Right Cause party), and we could not complete what we had set out to do. It is not in my nature to stop halfway," he said.
The Right Cause party finished with less than 1% of the vote.
Mr Prokhorov lost control of the party in September after a scandal in which he called a top Kremlin adviser, Vladislav Surkov, a "puppeteer who privatised the political system" and wanted to micromanage the party.
Today he said: "I found a clever solution - to become (Surkov's) boss."
Mr Prokhorov, who has been largely absent from the media since September, said he has "been working quietly and calmly building the infrastructure that I need to collect the 2.5 million signatures" to register in the race.
"We have a parliament that is completely leftist," said Mr Prokhorov.
He promised to build his programme "on a complete lack of populism" and call for reforms that would strengthen Russia's middle class.
Mr Prokhorov has previously called for pro-business reforms and advocated some controversial proposals - such as the release of jailed oil tycoon Mikhail Khodorkovsky and diversification of Russia's federal television network, currently state-controlled.
"I am not doing anything illegal. I am going in with my head held high and am not afraid," he said when asked if he feared sharing the fate of Khodorkovsky, who is thought to have paid the price for his political activity.
The Polys Gold metals miner chairman - consistently ranked as one of Russia's top five billionaires by Forbes magazine - was in 2010 estimated to have a fortune of $18 billion.