“All wars eventually end in peace,” he said. “But peace between Russia and Ukraine will not happen so long as Putin is in power.”

Born in Crimea into a modest, ethnic Russian family — his father, a native of the Ural Mountains region, worked as a driver before his death — Mr. Sentsov never paid much attention when he was growing up to friends who expressed hostility to Ukrainian rule of Crimea.

He said he did not care about politics and had always been far more interested, particularly after he took up writing and filmmaking, in exploring the inner lives of individuals and how “life is always more complicated and more difficult than it seems.”

His debut feature length film, “Gamer,” released in 2011 to critical acclaim, was shot in Crimea but skirts politics and focuses instead on a Russian-speaking teenager obsessed with video games at the expense of everything else, including his mother and his girlfriend. He eventually breaks his addiction.

Mr. Sentsov was preparing to shoot a second film, “Rhinoceros,” about a thick-skinned gangster who is not quite what he seems, when he got sucked into the protest movement against Ukraine’s former pro-Russian president, Viktor F. Yanukovych. He traveled to Kiev in December 2013 to join protesters in a central square known as Maidan and stayed there until after Mr. Yanukovych fled to Russia in late February 2014.

That experience, he said, made him realize just how Ukrainian, rather than Russian, he was in his values. “I never denied being Russian,” he said. “I can’t change the blood of my family. But I understood in Maidan that I’m a Ukrainian and will fight for Ukraine and die for it.”