The president of Ukraine turned to the vice prime minister for a key role after war began.

The youngest member of Mr. Zelensky's cabinet, Mr. Fedorov, immediately took charge of the defense against Russia. He began a campaign to get support from multinational businesses to sunder Russia from the world economy and to cut off the country from the global internet.

Mr. Fedorov used a mix of digital tools to achieve Russia's isolation. He used social media to pressure companies to stop doing business in Russia. A group of volunteer hackers wreak havoc on Russian websites. The ministry set up a fund that raised more than $60 million for the Ukrainian military.

Mr. Fedorov has become one of Mr. Zelensky's most visible lieutenants. Mr. Fedorov is trying to show how an outgunned country can use the internet, digital activism, and frequent posts on social media to undermine a foreign aggressor.

In his first interview since the invasion began, Mr. Fedorov said his goal was to make life so unpleasant and inconvenient for Russian citizens that they would question the war. He praised companies that had left Russia, but said they could go further by cutting off their app stores in the country.

He said that a technological and business blockade is an important part of stopping the aggression.

Mr. Fedorov brushed off concerns that his actions were alienating urban Russians who might be the most likely to oppose the conflict.

He said that as long as Russians are silent, they are complicit in the killing of our people.

Mr. Fedorov's work is not the only reason that multinational companies have left Russia, with the war provoking horror and outrage. The United States, European Union and others have imposed economic sanctions on Russia.

Peter Singer is a professor at the Center on the Future of War at Arizona State University.

No celebrity, let alone nation, has ever been more effective at calling out corporate brands to name and shame them into acting morally than the Ukrainians.

Mr. Fedorov sat in front of a wood-paneled wall during his interview on Zoom. He said that he gets about three to four hours of sleep a night, but that he often gets interrupted by an alert on his phone next to his bed. He said he was worried about his father, who was in intensive care after a missile hit the house next door.

He said that the war had come knocking on his door.

Mr. Fedorov grew up in a small town near the Dnieper River. He started a digital marketing company that designed online advertising campaigns.

He was hired by Mr. Zelensky, an actor who was making an unexpected run for Ukraine's presidency. Mr. Fedorov used social media to portray Mr. Zelensky as a youthful symbol of change.

Mr. Zelensky appointed Mr. Fedorov to be the minister of digital transformation. People could pay speeding tickets through a government app. Tim Cook, the chief executive of Apple, was one of the people Mr. Fedorov met in Silicon Valley last year.

Mr. Fedorov immediately ordered tech companies to leave Russia. He said that he made the decision with Mr. Zelensky's support.

Mr. Fedorov said that the choice was black and white.

He asked the companies to restrict access to their services in Russia. Apple stopped selling new products in Russia less than a week later.

Mr. Fedorov asked Mr. Musk for help in obtaining Starlink satellite internet systems that are made by Mr. Musk's company. Even if Russia damaged the country's main telecommunications infrastructure, the technology could help Ukrainians stay online. A shipment of Starlink equipment arrived in Ukraine two days after Mr. Musk contacted him.

Mr. Fedorov has exchanged text messages with Mr. Musk.

Mr. Fedorov had a call from a vice president of a company. Mr. Fedorov said that restricting access to certain features of Google Maps could be a safety risk. On Friday, the company blocked access to Russian state media on the internet, as well as other products and services.

The head of global affairs at Meta, which is the parent of Facebook and Instagram, has exchanged emails with Mr. Fedorov about the war.

They declined to comment. Mr. Musk didn't reply to the request for comment.

Mr. Fedorov said that public shaming has been effective because companies are emotional and rational.

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Many companies have stopped doing business in Russia. Scores of Russian businesses were using software made by companies like SAP and Apple should pull their app stores from Russia, he said.

The Russian government is cutting itself off from the world, including blocking access to social networking sites. Russian regulators said on Friday that they would restrict access to social media sites.

The Internet Protection Society, an internet freedom group in Russia, questioned whether Mr. Fedorov's tactics could have consequences.

Mr. Fedorov said it was the only way to awaken the Russians. He praised the work of Ukrainian-supporting hackers who have been coordinating with the Ukrainian government to hit Russian targets.

After cruise missiles started flying over my house and over houses of many other Ukrainians, we decided to go into counter attack.

Max Chernikov, a software engineer who is supporting the IT Army of Ukraine, said that Mr. Fedorov's work is an example of Ukraine's attitude against a larger Russian army.

He said that he acts like every Ukrainian.

Mr. Fedorov has a wife and a young daughter.

The truth is on our side, he said.

Mike Isaac and Daisuke Wakabayashi contributed to the report.