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Russian opposition leader Alexei Navalny announced Tuesday the formal start of his campaign to become Russian president in elections scheduled for March 2018. Here are some things to know about the politician who seems determined to challenge Vladimir Putin.

PUNCHY ANTI-CORRUPTION BLOG

Navalny first became known for exposes of Russian corruption that he posted on his blog in a sarcastic style. He started out targeting Russian business, and his early investigations were based on information he gleaned through his minority shareholdings in Russian companies.

He later moved on to major political figures. In recent years he has used property registries, social media trails and insider tip-offs to highlight the foreign properties owned by the Russian officials and the luxurious life led by many in the elite.

Powerful figures targeted by Navalny often simply deny his accusations, but revelations in his blog have led to resignations, a rare occurrence in Russian politics. In 2013, Vladimir Pekhtin, a senior figure in the ruling United Russia party, stepped down after Navalny alleged he owned an undeclared property in Florida worth over $2 million.

FIRST CROWDFUNDED ELECTION CAMPAIGN

Navalny ran against Sergei Sobyanin, the pro-Putin incumbent, in the 2013 Moscow mayoral elections and succeeded in raising over $2 million from a crowd-funding drive to pay for his campaign, which grew into a huge operation driven by enthusiastic young volunteers. Navalny himself made dozens of appearances at street rallies in the Russian capital while his supporters handed out pamphlets, bumper stickers and agitated on street corners.

A group of prominent businessmen announced they were backing Navalny in a sign that he was even gathering some support among the elite. Such a campaign was something new in Russian politics. Under Putin's rule, elections are rarely closely-fought and see little direct engagement with voters. While Navalny did not win the mayoral race, he surprised many observers by receiving more than 30 percent of the vote.

NATIONALISM

Navalny is widely backed by Russian liberals, but he does not hide his support for ethnic Russian nationalism. For many years he attended the Russian March, an annual demonstration also attended by extreme nationalist groups, and he has campaigned against the subsidies that Moscow provides to Chechnya and other republics in Russia's volatile North Caucasus.

In his presidential program he calls for new restrictions on immigration and the introduction of visas for migrants from ex-Soviet nations in the South Caucasus and Central Asia.

LEGAL CASES

Criminal investigations and trials have been a feature of Navalny's life since he became one of the leaders of Russia's anti-Putin protest movement in 2011. His supporters say all of the cases are politically motivated attempts to distract Navalny and discredit him in the eyes of ordinary Russians. He has served several short stints in jail.

Navalny is currently undergoing a re-trial in the city of Kirov after Russia's Supreme Court overturned his conviction on fraud charges in a 2013 case. If the court re-instates his conviction, it will bar him from running for public office.

In 2014, Navalny was also handed a suspended sentence on embezzlement charges, but that conviction doesn't bar him from being elected. Navalny's brother, Oleg, was jailed for three and a half years in the same trial, and remains behind bars.