But Peter Singer, a professor at the Center on the Future of War at Arizona State University, said Mr. Fedorov had been “incredibly effective” in calling for companies to rethink their Russia connections.

“No celebrity, let alone nation, has ever been more effective than Ukraine at calling out corporate brands to name and shame them into acting morally,” Mr. Singer said. “If there is such a thing as ‘cancel culture,’ the Ukrainians can claim to have honed it in war.”

In the 45-minute interview on Zoom, Mr. Fedorov, wearing a loosefitting gray fleece with black zippers, sat in front of a wood-paneled wall. He has gotten about three to four hours of sleep a night, he said, often interrupted every 30 minutes or so by alerts on the iPhone that he keeps next to his bed. He said he has been worried about his father, who has been in intensive care for the past week after a missile struck the house next door.

“I’ve brushed shoulders with the horror,” he said. “The war has come knocking on my door as well personally.”

Mr. Fedorov grew up in the small town of Vasylivka in southern Ukraine near the Dnieper River. Before going into politics, he started a digital marketing company called SMMSTUDIO that designed online advertising campaigns.

The work led him to a job in 2018 with Mr. Zelensky, then an actor who was making an unexpected run for Ukraine’s presidency. Mr. Fedorov became the campaign’s director of digital, using social media to portray Mr. Zelensky as a youthful symbol of change.

After Mr. Zelensky was elected in 2019, he appointed Mr. Fedorov, then 28, to be minister of digital transformation, putting him in charge of digitizing Ukrainian social services. Through a government app, people could pay speeding tickets or manage their taxes. Last year, Mr. Fedorov visited Silicon Valley to meet with leaders including Tim Cook, the chief executive of Apple.