Two former senior aides to President Trump's campaign pled not guilty Monday to criminal charges filed by special counsel, Robert Mueller, in the first prosecutions of his federal investigation into Russia's interference in the 2016 presidential election.

A federal grand jury charged that Trump's former campaign chairman, Paul Manafort, and his associate, Rick Gates, secretly worked to influence the U.S. government for pro-Russian sectors in Ukraine, then laundered their profits through overseas businesses and bank accounts.

It was also revealed Monday after the case was unsealed, former campaign foreign policy adviser, George Papadopolous, had already pled guilty to charges that he lied to the FBI about his meetings with a professor he knew was tied to the Russian government, who offered him "thousands of emails" in "dirt" on Trump's election opponent, Hillary Clinton.

The charges against Manafort and Gates include 12 counts of conspiracy, money laundering, failing to register as foreign agents while working for the Ukraine governement and making false statements to investigators.

But who exactly are these men and what is their place in the political world?

Here are 3 things to know about both Manafort and Gates:

Paul Manafort

1. Manafort is a political veteran. He has been a political consultant and lobbyist for decades. One of his early victories came after playing a significant role in helping Gerald Ford win a nomination during the 1976 convention despite a fight from Ronald Reagan and Bob Dole, according to ABC News. He went on to work for Reagan and George H.W. Bush years later and has a long history with the Republican Party. Manafort is regarded for his "polling techniques" and overall strategy, according to ABC News. Manafort has worked out of his own consulting firm since the 1980s.

2. Manafort is known for having worked with some controversial international leaders. His clients include former Filipino dictator, Ferdinand Marcos and military dictator of Zaire, Mobutu Sese Seko. Monday's charges mainly stem from Manfort's involvement with former president of Ukraine, Viktor Yanukovych, whose party had pro-Russia ties and was engaged in corruption. Manafort worked for Yanukovych from 2006 to about 2010, the year he helped him win the presidency, according to ABC News.

Yanukovych was taken out of power in 2014 after massive protests, but not before Manafort allegedly took nearly $13 million in undisclosed payments. The New York TImes published a report on Manafort's Ukraine secret cash payments last August which eventually led to his removal from the Trump campaign. Prosecutors allege Manafort and Gates-- who partnered with Manafort on business with Ukraine-- laundered $75 million overseas, money that came mostly from their work in Ukraine.

3. Manafort has deep ties to Russia but, it's important to note his relationships pre-date work for Trump. In addition to advising for Yanukovych, Manafort's company signed a multi-year agreement in 2006 with a Russian oligarch named Oleg Deripaska based on a 2005 proposal where Manafort outlined a strategy that would “greatly benefit the [Russian president Vladimir] Putin Government.”, according to the Washington Post. Deripaska has close ties to Putin. However, despite these ties, Mueller's investigation is specifically looking into Russian meddling in the 2016 elections. Mueller is required to investigate any matters that come up during the investigation which is where the current charges come in.

Rick Gates

1. Gates is the right-hand man to Manafort. He's worked as an associate at Manafort's consulting firm for decades -- beginning as an intern-- before today's charges. Gates followed Manafort to the Trump campaign, eventually serving as the deputy campaign manager, and stayed even after Manafort left the campaign. He is rumored to have signed off on Melania Trump's RNC speech which appeared to have been taken from Michelle Obama's speech to the 2005 DNC, according to ABC News.

2. Gates was closely intertwined with Manafort's business with Ukraine and criminal agenda to promote foreign interests, as well as with money laundering the cash from foreign clients overseas to avoid paying taxes. According to the indictment, although Manafort was central to the scheme, Gates played a prominent supporting role in the alleged crimes.

3. One of the charges against both Gates and Manafort is that they acted as "unregistered agents" of a Ukrainian political party that had pro-Russia motives, which is against the law. Manafort eventually registered in June of 2017 after facing pressure.