It was in that capacity, Mr. Akhmetshin said in an interview on Friday, that he accompanied a Russian lawyer, Natalia Veselnitskaya, to the meeting as part of an effort to amend an American law known as the Magnitsky Act that sanctioned Russians for human rights abuses. The 2012 law infuriated President Vladimir V. Putin of Russia, whose government retaliated by restricting adoptions of Russian children by Americans.
Mr. Akhmetshin, who wears his curly hair high in a manner that associates compare to the protagonist in the 1977 cult-classic horror film “Eraserhead,” said in the interview that he took part in the meeting at the request of Ms. Veselnitskaya. He said he had no ties to the Kremlin.
“I am a target of well-coordinated and financed smear campaign,’’ he said in a text message.
He described his time in the military as routine, serving from 1986 to 1988, like “millions of other Soviet boys.” He said he left the military with the rank of sergeant.
NBC News first reported Mr. Akhmetshin’s role in the Donald Trump Jr. meeting, but did not identify him. He first confirmed to The Associated Press that he attended the meeting.
Mr. Akhmetshin has boasted to associates that he had served in the military with a group known as the Osoby Otdel, or Special Section, which in the Soviet period was a division of the K.G.B. The group was distinct from the G.R.U., or Main Intelligence Directorate of the defense ministry, an organization with which he has denied any affiliation.
Those who know Mr. Akhmetshin describe him as a devoted parent, ferrying his school-age daughter to extracurricular activities around Washington. He speaks with a slight accent and is a voracious reader of classic American novels.