China's most famous living artist is also one of its most dogged political dissidents. After spending 81 days in detention last year, Ai Weiwei, 55, re-emerged unbowed, tangling with officials over a dubious $2.4 million tax bill and continuing to speak out against authoritarian rule. Ai's struggle against the state is itself becoming a form of performance art: because his passport was confiscated, he was unable to attend the Oct. 7 opening of a major retrospective of his art held at the Smithsonian in Washington, D.C. His absence generated headlines around the world, effectively turning a muzzle into an amplifier.