Alexei Navalny has been outspoken in his criticism of the Russian government for years.
The former real estate lawyer became a shareholder activist and anti-corruption campaigner before running for Moscow's mayoralty, and pushing for changes to Russia's political system.
None of this endeared him to the federation's premier, Vladimir Putin.
After being poisoned last year, almost certainly by Russian agents, last week Navalny returned to Moscow and was arrested.
His return sparked anti-government protests leading to thousands of arrests across the country.
To discuss the latest we're joined by Anton Troianovski, the Moscow correspondent for The New York Times.