WASHINGTON — He is a veteran of the Red Army, photographed in the 1980s with fellow soldiers in a Russian birch forest. He collects fine art, likes opera and owns a nearly $2 million townhouse in trendy Logan Circle, in the center of Washington. He often zips around the city on a bright orange bicycle.

On Friday, Rinat Akhmetshin, the Soviet army veteran, revealed another detail of an exotic life: He was one of the people at the meeting Donald Trump Jr. had with a Russian lawyer at Trump Tower on June 9, 2016.

The presence of Mr. Akhmetshin adds another development to the evolving narrative about the gathering, which Donald Trump Jr. arranged after learning that a Russian lawyer claimed to have damaging information about Hillary Clinton. The news of Mr. Akhmetshin’s attendance shows how the story of the meeting keeps changing and has increased pressure on the White House to offer a more comprehensive account of what happened.

Mr. Akhmetshin, a naturalized American citizen who talks openly of his past in a K.G.B. counterintelligence unit focused on hunting spies in the Russian military, is well known in diplomatic and media circles in Washington, where he has worked for years on behalf of business and political interests in Russia and other former Soviet states.