The retired lieutenant general, who resigned in February, is believed to be at the center of various ongoing investigations into the Trump campaign's ties and possible collusion with the Russian government during the presidential campaign.
Newly appointed special counsel Robert Mueller has been charged with investigating the dealings between the Trump campaign and Russian officials.
Here is a timeline of the various revelations relating to Flynn and Comey.
Dec. 25, 2016: Flynn texts the Russian ambassadorMichael Flynn and Russian ambassador Sergey Kislyak exchanged holiday greetings over texts, according to White House press secretary Sean Spicer.
Dec. 29, 2016: Sanctions added and a follow up callFiring back at alleged Russian efforts to influence the election, the Obama administration announced it was expelling 35 Russian intelligence operatives from the United States and placing sanctions on five Russia entities.
The Russian ambassador sent Flynn a text message asking whether they could talk over the phone. Flynn accepted the invitation and the two spoke by phone that day, according to Spicer.
Flynn and Kislyak's call "centered around the logistics of setting up a call with the president of Russia and the president-elect after he was sworn in," Spicer said, adding, "They exchanged logistical information on how to initiate and schedule that call. That was it. Plain and simple."
Spicer stressed to ABC News that Flynn and Kislyak did not discuss the sanctions.
Jan. 15, 2017: Pence says what Flynn told himIn an interview on CBS' "Face the Nation," then-Vice President-elect Mike Pence said that Flynn told him that conversation centered around "Christmas wishes" and "sympathy for the loss of life in the airplane crash that took place" Dec. 25.
"It was strictly coincidental that they had a conversation," Pence said. "They did not discuss anything having to do with the United States' decision to expel diplomats or impose censure against Russia."
A senior administration official told ABC News in March that Pence's information had come from speaking with Flynn directly.
Jan. 21, 2017: Another Flynn callA follow-up phone call occurred between Flynn and Kislyak to discuss setting up a call between Trump and Russian President Vladimir Putin, Spicer clarified in a press briefing on Jan. 23.
Jan. 22, 2017 - Trump and Comey appear chummyTrump welcomed Comey to the White House during a reception for law enforcement and first responders.
Trump pointed out Comey, calling him "James," and said with a chuckle, "He's become more famous than me." Comey went up to Trump and shook the president's hand.
Jan. 23, 2017: Explanation for the callsDuring the White House press briefing, Spicer reiterated that the only topics Flynn and Kislyak discussed were holiday greetings, the deadly December plane crash carrying the Russia military choir, the conference in Syria on ISIS and to set up a call between Putin and Trump.
Jan. 26, 2017: Yates' warningThe Justice Department's then-acting Attorney General Sally Yates informed White House counsel Don McGahn that they were misled and expressed concerns that Russia might try to blackmail Flynn.
After he had been informed by the DOJ, McGahn briefed the president and a small group of aides on Flynn. The president asked McGahn to conduct a review to determine whether there was a legal situation. McGahn determined "within several days" there was not a legal issue, Spicer said, without providing further details.
Feb. 9, 2017 - Subjects of talks revealedThe Washington Post reported that Flynn discussed sanctions with Russia's ambassador to the United States before Donald Trump took office. The Post reported that on Feb. 8 Flynn denied twice that he discussed sanctions with Kislyak.
Current and former U.S. officials confirmed to ABC News that Flynn and Kislyak spoke about Russia sanctions, but were unable to say that explicit promises were made to lift the sanctions.
Feb. 10, 2017 - Flynn's story begins to changeA senior administration official told ABC News that Flynn didn't recall the issue of sanctions ever coming up in his conversations with Kislyak, but "isn't completely certain."
Flynn called Pence to apologize for misleading him about his conversation with the Russian ambassador, a senior White House official later told ABC News' Jonathan Karl.
Feb. 11, 2017 - Pence and Flynn talkPence spoke twice with Flynn on Friday Feb. 10, a senior administration official confirmed to ABC News on Feb. 11.
Feb. 13, 2017 - Flynn resignsHouse Minority Leader Nancy Pelosi, D-Calif., released a statement calling on Flynn to be "fired immediately." "We have a national security adviser who cannot be trusted not to put Putin before America," the statement read.
Kellyanne Conway, counselor to the president, told MSNBC that Flynn "enjoy[s] the full confidence of the president." An hour later, however, White House chief of staff Reince Priebus released a statement that said, "the president is evaluating the situation."
That night, Flynn resigned from his position as national security adviser. The retired lieutenant general released a letter of resignation in which he apologized to Trump and Pence.
"Unfortunately, because of the fast pace of events, I inadvertently briefed the Vice President Elect and others with incomplete information regarding my phone calls with the Russian Ambassador," Flynn's letter read. "I have sincerely apologized to the President and the Vice President, and they have accepted my apology."
Feb. 14, 2017 -- Firing confirmedSpicer, in a White House press briefing, confirmed that the president asked for Flynn's resignation.
Feb. 15, 2017 -- The Trump campaign was being 'looked into' ahead of the electionSources familiar with the matter confirmed to ABC News that in the time leading up to the presidential election, U.S. authorities were looking into communications between several Trump associates and suspected Russian intelligence officials.
The New York Times first reported that according to several current and former U.S. officials, several Trump associates inside and outside the campaign -- including former campaign chairman Paul Manafort -- had repeated contact with senior Russian intelligence officials in the year before election.
Manafort told ABC News on Feb. 15 that the report published in the Times is "completely ridiculous."
March 1, 2017: Reports about Sessions' meetings with RussiansNews breaks that Attorney General Jeff Sessions met with the Russian ambassador twice in 2016, which appears to contradict his statement during his confirmation hearing.
A White House official responded to ABC News, dismissing the claims as an attempt to deflect from Trump's "successful" address to a joint session of Congress on Tuesday, Feb. 28.
March 2, 2017: Sessions recuses himselfSessions announced that he would recuse himself from any existing or future probes related to any campaigns for president.
"Let me be clear: I never had meetings with Russian operatives or Russian intermediaries about the Trump campaign," Sessions told reporters. "And the idea that I was part of a continuing exchange of information during the campaign between Trump surrogates and intermediaries to the Russian government are false."
March 10, 2017 - Flynn's team warned about his foreign agent status
A lawyer for retired Flynn contacted an attorney for the Trump transition team about whether Flynn needed to register as a foreign agent before taking the role of national security adviser -- from which he was later forced to resign, Spicer announced at a press briefing.
Pence -- who had been the chairman of the transition team -- said that the first time he heard of the lobbying ties was the week of March 10 and not during the transition.
"Let me say hearing that story today was the first I heard of it and I fully support the decision that President Trump made to ask for General Flynn's resignation," Pence said in an interview with Fox News on March 9.
March 20, 2017 - Comey confirms FBI's investigation into potential Trump-Russia tiesDuring a five-hour hearing on Capitol Hill, Comey confirmed to the House Intelligence Committee that the FBI was investigating Russia's interference in the 2016 election, including any possible links or coordination between Trump campaign associates and the Russian government.
March 30, 2017 - Flynn wants immunityFlynn is in discussions to testify in front of the Senate and House congressional investigations into Russian meddling in the 2016 election and is seeking "assurances against unfair prosecution," Flynn's lawyer said in a statement.
"General Flynn has a story to tell, and he very much wants to tell it, should the circumstances permit," Flynn's lawyer Robert Kelner said.
The Senate and House Intelligence Committees have not publicly indicated willingness to grant Flynn's request.
April 12, 2017 - Trump hints at Comey's futureTrump told Fox Business in an interview that "it's not too late" to dismiss Comey from his position as head of the FBI. Presidents have the authority to fire FBI directors, which has only happened once before, in 1993."No it's not too late. But you know, I have confidence in him," Trump said. "We'll see what happens."
May 1, 2017 - Comey meets with RosensteinThe last meeting between Comey and Deputy Attorney General Rod Rosenstein was a week before Comey was fired. During their meeting the two "talked about issues unrelated to what is being reported" and resources for the Russia probe were not discussed, according to a DOJ spokeswoman.
May 3, 2017 - Comey explains his Oct. 28 letterDuring an oversight hearing in front of the Senate Judiciary Committee, Comey was asked several questions about his decision to send the Oct. 28 letter to Congress.
"It makes me mildly nauseous to think that we might have had some impact on the election, but honestly, it wouldn't change the decision," Comey said.
According to a statement released to White House reporters, Trump "was strongly inclined to remove" Comey after his testimony.
May 8, 2017 - Comey asks for fundsComey briefed some members of the Senate Intelligence Committee that he had asked for more money and manpower from the DOJ. Comey's request was made directly to Deputy Attorney General Rosenstein - the man who recommended his firing. However, this is not known until May 10.
DOJ spokeswoman Sarah Flores said on May 10 that these reports were "100 percent false." "It didn't happen," Flores said in a statement.
White House officials said in a statement that Trump met with Sessions and Rosenstein on Monday to discuss reasons for firing Comey.
May 9, 2017 - Comey is firedRosenstein wrote a memorandum, dated May 9, to Sessions, criticizing Comey's handling of the Clinton email investigation as well as his July 5 press conference on the FBI's findings in the Clinton probe.
"I cannot defend the director's handling of the conclusion of the investigation of Secretary Clinton's emails, and I do not understand his refusal to accept the nearly universal judgment that he was mistaken," Rosenstein wrote.
Shortly after 5 p.m. ET, President Trump called several members of Congress to inform them of his decision.
According to Spicer, Trump reached out to House and Senate leadership. He called Speaker Paul Ryan and left a message for House Minority Leader Nancy Pelosi. He also spoke to Senate Minority Leader Chuck Schumer and reached out to Senate Majority Leader Mitch McConnell as well as Sens. Lindsey Graham, Bob Goodlatte, Chuck Grassley and Dianne Feinstein.
Around 5:40 p.m., news broke that Comey was fired. A statement from the White House said that Trump informed Comey he had been "terminated and removed from office" and the search for a new FBI director will "begin immediately."
A White House official confirmed to ABC News that Keith Schiller, the president's longtime bodyguard and Oval Office director of operations, hand-delivered Trump's termination letter to FBI headquarters.
Comey, who was in Los Angeles for bureau travel, learned of his firing from TV reports. The letter from Trump was read to him over the phone, two FBI sources told ABC News. Comey was scheduled to be the keynote speaker at a LA recruitment event but canceled his speech.
The New York Times reported that senior White House and DOJ officials were instructed to build a case against Comey and Sessions was assigned to come up with reasons to justify firing Comey.
Spicer said the letters written by Rosenstein and Sessions convinced Trump to fire Comey.
The president made the decision to let Comey go "pretty quickly" after receiving the recommendations, deputy press secretary Sarah Huckabee Sanders told Fox News later that night.
Trump met with acting FBI director Andrew McCabe in the Oval Office that evening. McCabe held a conference call with the heads of FBI field offices across the country.
May 11, 2017 - Trump says he planned to fire Comey ahead of the DOJ recommendationDuring an interview with NBC's Lester Holt, Trump contradicted previous White House statements for Comey's firing, saying that he planned on firing him regardless of what the DOJ suggested.
"I was gonna fire regardless of recommendation," Trump said.
Trump went on to say Comey is "a showboat, he's a grandstander," and that the FBI has been in "virtual turmoil."
He also reiterated the claim that Comey had told Trump three times that he was not under investigation -- a claim first made publicly in Comey's dismissal letter.
"I said, if it's possible would you let me know, am I under investigation? He said, 'You are not under investigation,'" Trump said in the NBC interview.
Later that day, The New York Times reported that two Comey associates said Trump asked for a pledge of loyalty from the FBI director.
May 12, 2017 - Trump tweets veiled threat to leak 'tapes'Trump went on a Twitter tear, taking aim at both the media and Comey.
"James Comey better hope that there are no 'tapes' of our conversations before he starts leaking to the press!" he wrote.
May 13, 2017 - Trump denies loyalty pledge"I didn't ask that question," Trump said in an interview with Fox News' Jeanine Pirro that aired May 13.Trump, however, said it "wouldn't be a bad question to ask."
May 15, 2017 - Report alleges Trump shared confidential information with RussiansTrump reportedly shared classified information with Russian Foreign Minister Sergey Lavrov and Russian ambassador to the U.S. Sergey Kislyak when they met in the White House on May 10. The Washington Post first reported the news, and while a number of White House surrogates first denied the entirety of the story, their interpretations changed over time.
May 16, 2017 -- Comey's paper trail revealed, memo says Trump told him to stand downTrump started the day by seemingly admitting that he did share some information with the Russian officials but denied any wrongdoing.
"As President I wanted to share with Russia (at an openly scheduled W.H. meeting) which I have the absolute right to do, facts pertaining to terrorism and airline flight safety. Humanitarian reasons, plus I want Russia to greatly step up their fight against ISIS & terrorism," he wrote in two tweets.
A major concern that was raised in the wake of the disclosure was whether or not Trump's revelations put the source of the information and the methods of collection in jeopardy. National Security Adviser H.R. McMaster said that Trump "wasn't even aware" where the information came from when he shared it. Israel was later confirmed to be the source of the intelligence.
Reports about a memo that Comey wrote shortly after his Jan. 22 meeting with Trump purportedly said that he was asked by the president to drop the bureau's investigation into Flynn. Details of the memo, first reported by The New York Times on Tuesday, were later confirmed to ABC by sources close to Comey.
In the memo, which Comey shared with top FBI associates, he wrote that Trump said, "I hope you can let this go," referring to the inquiry into Flynn's actions. "I hope you can see your way clear to letting this go, to letting Flynn go," said Trump, according to a source who read the memo. "He is a good guy. I hope you can let this go."
Multiple sources who worked closely with Comey, including at the Justice Department, say he is known for his contemporaneous and thorough note-taking. "He documents everything," one source said.
May 17, 2017 - Special counselor namedThe DOJ announced that a special counsel has been appointed to investigate Russian interference into last year's presidential election.
Former FBI Director Robert Mueller was assigned by Deputy Attorney General Rod Rosenstein to "oversee the previously-confirmed FBI investigation of Russian government efforts to influence the 2016 presidential election, and related matters."
Mueller will have 60 days to put together a budget for resources to conduct the investigation and that budget must be approved by Rosenstein. Attorney General Sessions previously recused himself from all matters related to the presidential campaign.
May 18, 2017 -- Pence stands by earlier statementsPence stood by his March claim that he learned of Flynn's lobbying for the first time through news reports of his ties to Turkey, despite a May 17 New York Times report that Flynn informed the transition team weeks before the inauguration that he was under federal investigation for those lobbying ties.
Editor's note: An earlier version of this story incorrectly stated the month Flynn resigned.