I’ll start with the Wikipedia introduction:
Alexei Anatolievich Navalny (Russian: Алексей Анатольевич Навальный, born June 1976) is a Russian lawyer, politician, and political and financial activist. Since 2009, he has gained prominence within Russia, and notably within the Russian media, as a critic of corruption in Russia, and especially of Russian leader Vladimir Putin. He has used his LiveJournalblog to organize large-scale demonstrations to address these issues. He also regularly writes articles in several Russian publications, such as Forbes Russia. In a 2011 interview with Reuters, he stated that Putin’s political system is so weakened by corruption that Russia could face an Arab Spring-style revolt within five years.
Navalny was named “Person of the Year 2009” by Russian business newspaper Vedomosti. In 2011, the BBC described Navalny as “arguably the only major opposition figure to emerge in Russia in the past five years”. In 2012, The Wall Street Journal called him “the man Vladimir Putin fears most”. He was the only Russian to be named in Time magazine’s 2012 list of the world’s 100 most influential people.