Russian opposition politician Alexei Navalny was in a coma in a Siberian hospital on Thursday after drinking a cup of tea that his spokeswoman said she believed was laced with poison.
Here are some key details about Navalny:
A leading anti-corruption campaigner, Navalny was one of the first protest leaders arrested when demonstrations against Russian President Vladimir Putin took off in December 2011.
He soon became established as one of the leaders of the Russian opposition, though internal squabbling and policy differences among different factions have often divided the movement.
He has been barred from taking part in elections on various grounds which he says are trumped up by the Kremlin, but has used social media to mobilise crowds of mostly young protesters.
Navalny is best known inside Russia for producing detailed and high-impact investigations into official corruption which he posts on his YouTube channel. They gain millions of views.
BRUSHES WITH AUTHORITY
He has been repeatedly detained for organising public meetings and rallies and was barred from leaving Moscow in July this year while authorities investigated him for suspected slander.
His anti-corruption foundation has been found guilty of violating a "foreign agent" law and he was convicted of corruption by Russian authorities in 2013. His supporters say it and other cases against him are politically motivated.
The son of an army officer, he was born on June 4, 1976 and grew up mainly in Obninsk, about 100 km (62 miles) southwest of Moscow. He has a law degree, and spent time in the United States on a fellowship at Yale.
He also studied securities and exchanges and bought small stakes in some of Russia's biggest companies to demand greater transparency for shareholders and the public.
He was once an outspoken Russian nationalist, expelled from a liberal opposition party for his views.