U.S. Army Lt. Col. Alexander Vindman has been an infantry officer in multiple overseas tours, and received a Purple Heart when he was wounded in Iraq by a roadside bomb. He’s served in U.S. embassies in Kyiv and Moscow, and worked on Russian politico-military affairs at the Pentagon.

But it is his most recent tour as the National Security Council’s top Ukraine expert at the White House that has placed him squarely in the national spotlight, as the Democratic-controlled House of Representatives pushes ahead with its impeachment inquiry aimed at President Donald Trump.

Vindman listened in July 25 as Trump talked with Ukraine President Volodymyr Zelenskiy and asked him for “a favor” — initiate investigations of one of Trump’s top 2020 Democratic challengers, former Vice President Joe Biden, and his son, Hunter, who until earlier this year was on the board of a Ukrainian natural gas company.

Vindman told impeachment investigators he was so troubled by Trump’s request to Zelenskiy to intervene in the U.S. political scene that he reported the president’s comments to his superiors.

Now 44, Vindman and his twin brother, Yevgeny, were 3-years-old when they and their family fled Ukraine, then part of the Soviet Union, for the United States. His brother is also an Army lieutenant colonel and a lawyer handling ethics issues for the National Security Council.

Vindman told House investigators that “upon arriving in New York City in 1979, my father worked multiple jobs to support us, all the while learning English at night. He stressed to us the importance of fully integrating into our adopted country.”

“For many years,” Vindman said, “life was quite difficult. In spite of our challenging beginnings, my family worked to build its own American dream. I have a deep appreciation for American values and ideals and the power of freedom. I am a patriot, and it is my sacred duty and honor to advance and defend our country, irrespective of party or politics.”

He said he has served more than 20 years as a U.S. military officer and diplomat “in a nonpartisan manner, and have done so with the utmost respect and professionalism for both Republican and Democratic administrations.”

Trump described Vindman as a “Never Trumper” and questioned why he was being allowed to testify in the impeachment hearing.