Artem Shmyrev had everyone fooled. The Russian intelligence officer seemed to have built the perfect cover identity. He ran a successful 3-D printing business and shared an upscale apartment in Rio de Janeiro with his Brazilian girlfriend and a fluffy orange-and-white Maine coon cat.

But most important, he had an authentic birth certificate and passport that cemented his alias as Gerhard Daniel Campos Wittich, a 34-year-old Brazilian citizen.

After six years lying low, he was impatient to begin real spy work.

“No one wants to feel loser,” he wrote in a 2021 text message to his Russian wife, who was also an intelligence officer, using imperfect English. “That is why I continue working and hoping.”

He was not alone. For years, a New York Times investigation found, Russia used Brazil as a launchpad for its most elite intelligence officers, known as illegals. In an audacious and far-reaching operation, the spies shed their Russian pasts. They started businesses, made friends and had love affairs — events that, over many years, became the building blocks of entirely new identities.

Major Russian spy operations have been uncovered in the past, including in the United States in 2010. This was different. The goal was not to spy on Brazil, but to become Brazilian. Once cloaked in credible back stories, they would set off for the United States, Europe or the Middle East and begin working in earnest.

The Russians essentially turned Brazil into an assembly line for deep-cover operatives like Mr. Shmyrev.