The firm, called Black, Manafort, Stone and Kelly, was known for its work to help improve the image of controversial politicians, including Ferdinand Marcos of the Philippines, Mobutu Sese Seko of the Democratic Republic of the Congo and the Russian-aligned former president of Ukraine, Viktor Yanukovych.
Gates joined the Trump campaign in the spring of 2016 and became Manafort's deputy. It was there where he became close to many of Trump's confidants. He remained with the campaign even after Manafort's ouster. Gates then worked on Trump's inaugural committee and co-founded the pro-Trump nonprofit group America First Policies.
In March, Gates was pulled into the Mueller inquiry when the special counsel's office filed a motion that claimed the former campaign aide had contact with a former agent of the Russian intelligence service in 2016. This came after Gates pleaded guilty to lying and conspiring against the United States, which could lead to possibly six years in prison. A sentencing date has yet to be announced.
For Stone, this is another potential hurdle in an ongoing investigation that continues to focus on him, among others.
Sam Nunberg, a former Trump campaign advisor, also said he was asked about Stone's involvement with Wikileaks during his interview before Mueller's grand jury in March.
"Roger is certainly a subject," Nunberg said. "The fact that Roger hasn't been called in and the special counsel continues to ask questions about Roger's possible activities during the election shows that at the very least he's a subject."
Stone allegedly met with Assange, the Wikileaks founder, in August 2016. In an email leaked to The Wall Street Journal, Stone said, "I dined with my new pal Julian Assange last nite."
Stone has denied that he has met with the Wikileaks founder and said the email was in jest.
During the 2016 campaign, Wikileaks published emails allegedly stolen from the Democratic National Committee's servers by a Russia-linked hacker known as "Guccifer 2.0."