National Security Adviser Michael Flynn (C) sits before U.S. President Donald Trump and Japanese Prime Minister Shinzo Abe hold a joint press conference at the White House on February 10, 2017 in Washington, DC. (Mario Tama/Getty Images)

When Michael Flynn served as a top adviser during Donald Trump's 2016 presidential campaign, he negotiated deals with a Turkish lobbyist through Ukrainian-born businessman Dmitri "David" Zaikin, who has connections both with Vladamir Putin and Trump.

Flynn's activities with undisclosed foreign lobbyists came under increased scrutiny as Senate, Congressional, and FBI investigations heat up as to whether or not the Trump campaign colluded with Putin's government to hack and influence the election. Zaikin could be an important link between Putin and Trump's campaign.

READ: Russians Viewed Michael Flynn As A Close Friend, Sources Say While Trump Meets Saudi King In Riyadh

Zaikin was born in Soviet-era Ukraine and a former executive of Russian energy and mining companies. He linked Flynn to a Turkish businessman named Ekim Alptekin, who gave Flynn $600,000 to push Turkey's agenda in Washington just before Trump picked him to be national security adviser, according to a report by Politico in April.

Born in 1967 in Soviet-era Ukraine, Zaikin fled the USSR to Canada in 1990 becoming a real estate agent and broker. In 2002, he became chairman of Siberian Energy Group, whose company’s archived website noted his "extensive ties to Russia’s business community, as well as to federal and regional government authorities."

"David was on the inside track," Jordan Silverstein, who worked for a firm doing investor relations for Siberian Energy Group, told Politico in an article published Tuesday. "He seemed like an international man of mystery."

Often Zaikin's connection to Putin's government was indirect. For instance, Siberian Energy Group was connected to the governor of the Western Siberian province of Kurgan, who reported to Putin. With his inside track that featured one foot in the real estate business and the other foot in energy and oil, he began to promote another brand: Trump and Trump hotels.

READ: What Is The Fifth Amendment? Former National Security Adviser Michael Flynn To Deny Subpoena

In 2005, Zaikin told the Globe and Mail newspaper about a new development he was promoting: the Trump International Hotel and Tower. The newspaper reported that Zaikin called his "top five international clients" and four agreed to buy.

"When this project was announced I instantly became a strong believer that it would be a significant winner," Zaikin told the newspaper in an innocuous piece. "I have stayed at Trump Hotels and seen how other similar projects went in New York, Chicago and Las Vegas."

Zaikin said his reason for a sudden interest in the Trump brand was because "there is nothing else like it."

"No other project offers the range of suites, the amenities and the luxury and quality of construction," he said lauding the Trump brand with being an international city. "Toronto has become a world-class, international city."

In 2011, Zaikin moved to London and he began to get involved in politics, advising ruling parties in Turkey, Albania, and Macedonia, and lobbied for those parties in the United States. He met Alptekin in 2015 while helping to run pro-Turkish nonprofit groups.

Alptekin would eventually use Zaikin's connections to lobby Flynn while he was working as an advisor to Trump's campaign and just before he was named as National Security Adviser. Flynn was fired from his post in February for not disclosing meetings with Russian Ambassador Sergey Kislyak.

Special Counsel Robert Mueller has been looking into the connection between Flynn and his role in the Trump campaign and the Russian government.