Dmitri Utkin, a Leader of the Wagner Mercenaries

Dmitri Utkin, a longtime lieutenant to the Russian mercenary leader Yevgeny V. Prigozhin and the man whose nom de guerre inspired the name of their private military outfit, Wagner, was widely believed to have died along with him in a plane crash in Russia on Wednesday. He was 53.

Mr. Utkin’s death has not been officially confirmed by the Russian authorities or Wagner, but he was listed as a passenger on a plane that went down in a field as it was flying from Moscow to St. Petersburg.

Mr. Utkin, a veteran Russian military officer, was closely intertwined with Wagner from its emergence as a fairly modest fighting group a decade ago to its evolution into a brutal, armed-to-the-teeth force willing to do the Kremlin’s bidding from Africa to the Middle East to, most recently, the hottest spots on the Ukrainian battlefield.

But his exact role was a bit murky.

Over the years, Mr. Utkin was at times referred to as the “founder” of Wagner, which first came to public attention during early forays against Ukraine ordered by President Vladimir V. Putin in 2014, a precursor to the full-scale invasion of 2022. Wagner mercenaries fought alongside pro-Russian separatists in the Donbas region, and were commanded by Mr. Utkin.

Whether he was the group’s actual founder, though, became less and less certain over time. “While Dmitry Utkin has been widely presented as the front man and ‘principal’ for the Wagner PMC, there is ample data suggesting that his role was more of a field commander,” a report issued in 2020 by the investigative website Bellingcat said. Open-source data, it said, strongly suggested that Mr. Utkin was “not in the driver’s seat of setting up this private army” but rather was a “hired gun.”

Part of the challenge in understanding his role was that while Mr. Prigozhin was outspoken of late, delighting in seizing the spotlight and denouncing rivals in the Russian regular military, Mr. Utkin was rarely seen in public. Bellingcat called him “camera shy.”

In many respects, though, his influence on the culture of Wagner appeared clear.

Mr. Utkin, a retired Russian Special Forces officer, was described as fascinated by Nazi history. The mercenary group’s name — and, before that, Mr. Utkin’s military call sign — were said to have been inspired by the composer Richard Wagner, a favorite of Hitler’s. Some of the group’s fighters seemed to share that ideology: Ancient Norse symbols favored by white supremacists have been photographed on Wagner equipment in Africa and the Middle East.

Mr. Utkin, who was born in 1970, served with the military in two wars in Russia’s restive Chechnya region and was in the G.R.U., the Russian military intelligence agency until 2013, according to a 2020 report from the Center for Strategic and International Studies. After that he commanded a Spetsnaz special forces unit and attained the rank of lieutenant colonel, the report said.

But it was as part of Wagner that he attained notoriety.

In 2015, a year after helping shear off sections of eastern Ukraine, the Wagner group turned its attention to Syria, tasked by the Kremlin not only with bolstering President Bashar al-Assad in the country’s civil war but also with seizing oil and gas fields, American officials have said. Wagner operatives have also fought in Sudan, Central African Republic, Mali and Mozambique, extending Russian influence in Africa by proxy.

Officially, the Kremlin denied ties to Wagner, but in 2016, Mr. Putin awarded Mr. Utkin military honors at a banquet.

A year later, the United States bestowed its own recognition of sorts: It imposed sanctions on Mr. Utkin over his activities with Wagner, specifically, recruiting soldiers to join separatist forces in Ukraine. (Britain, the European Union and Canada also imposed sanctions on Mr. Utkin and Mr. Prigozhin.)

In 2022, after Russia’s full-scale invasion of Ukraine began, Wagner’s fighters took on a major role, most notably in the bloody, nearly yearlong battle for Bakhmut where Mr. Prigozhin’s mercenaries ultimately claimed victory.

But the glory was fleeting.

Mr. Prigozhin grew increasingly incensed at what he called the incompetence of Russian military leaders, and while he was careful to profess loyalty to Mr. Putin, he spared no words in his denunciations of the president’s underlings. In late June, words turned to action, and Wagner forces briefly took up arms against Russian soldiers, outraging the Russian president.

Inside and outside the country, many watched closely to see what fate might befall Mr. Prigozhin.

In the days that followed, Mr. Utkin stayed by the Wagner chief’s side. And the following month, video emerged that appeared to show Mr. Prigozhin delivering a speech to Wagner fighters who had relocated to Belarus. After finishing, he turned the floor over to Mr. Utkin, who this time did not maintain his customary discretion.

“This is not the end,” Mr. Utkin said.