MOSCOW — A Russian opposition activist has been released from prison after serving his term.

Sergei Udaltsov’s release was announced Tuesday by his wife Anastasia, who said on Facebook that he’s “full of optimism and positive emotions.”

Udaltsov has served 4½ years on charges related to his role in staging a May 2012 protest rally against President Vladimir Putin that ended in clashes with police.

Udaltsov was among key organizers of a series of massive street protests in Moscow in 2011-2012 against Putin’s return to the presidency. Following Putin’s inauguration, the Kremlin has cracked down on its foes with a slew of laws that put tight restrictions on holding demonstrations and curbed the activity of non-governmental organizations.