With those words, President Donald J Trump became only the second US commander-in-chief to fire his FBI director.
With those words, Donald Trump became only the second president to fire his FBI director.
And so a firestorm of shifting explanations, claims and counter-claims was unleashed.
But why was he dismissed?
So what are the possible reasons for the sacking - and what has been said about them?
1) The Clinton emails
1) The Clinton emails
This was the first official reason. The president opened his termination letter to Mr Comey by referring to letters by his Attorney General Jeff Sessions and Mr Sessions' deputy, Rod J Rosenstein, outlining what they saw as failures in Mr Comey's time in office.
This was the first official reason. The president opened his missive to Mr Comey by citing a damning letter from Deputy Attorney General Rod Rosenstein that accused the now-former FBI director of "serious mistakes".
Mr Rosenstein's letter says "the FBI's reputation and credibility have suffered substantial damage, and it has affected the entire department of justice".
Among other things, it said Mr Comey had "usurped" the authority of the former attorney general by announcing last July the closure of the inquiry into Hillary Clinton's use of a private email server.
His letter focuses on the fallout from an FBI investigation, now closed, into Hillary Clinton's use of a private email server to store sensitive information while secretary of state.
The letter faulted him for "gratuitously" releasing "derogatory information" about the subject of an investigation - Mrs Clinton.
"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," Mr Rosenstein goes on to say.
It even criticised his public reopening of the inquiry 11 days before the election, a step which some say contributed to Mr Trump's shock victory over Mrs Clinton.
So did Mr Comey act correctly?
At the time Mr Trump had praised Mr Comey's unusual move, saying it "took guts".
"The director was wrong to usurp the attorney general's authority on 5 July 2016, and announce his conclusion that the case should be closed without prosecution," Mr Rosenstein's letter says.
Mr Comey chose to announce there would be no investigation because, the letter says, "he believed Attorney General Loretta Lynch had a conflict".
While this was not customary, Mr Comey explained why he took the responsibility ahead of Ms Lynch. He said he did it because she had recently generated adverse headlines by having a meeting with ex-President Bill Clinton on an airport runway. They said it was a casual encounter but she was accused of a conflict of interest.
It is also unusual for the FBI to go public with an investigation, especially during an election campaign. Mr Comey did that not once but twice.
He justified it by saying if he had not come forward, he could have been guilty of concealment.
What was Clinton FBI probe about?
Mrs Clinton's supporters cried foul when it emerged that the Trump election team was also under investigation by the FBI, but Mr Comey never divulged that until a long time after the election.
And as Mr Trump has pointed out, Democrats who said they had lost confidence in Mr Comey last year, are now angered over his abrupt firing. "Phony hypocrites", he called them.
One key question though - if this was indeed the real reason Mr Comey was fired, why did the White House wait until now? The Clinton investigation was closed in early November, and Mr Trump has been in office since 20 January.
When asked why he didn't fire him earlier, deputy White House press secretary Sarah Huckabee Sanders said "I believe the president wanted to give Director Comey a chance."
2) 'He wasn't doing a good job'
2) 'He wasn't doing a good job'
This was President Trump's first in-person explanation, given from the Oval Office on Wednesday.
This was President Trump's first in-person explanation, given from the Oval Office in an interview with NBC News.
It was reiterated in his Thursday NBC interview when he said the FBI had been "in turmoil... everybody knows that".
He said he had already decided to fire Mr Comey, "regardless of recommendation" as the FBI had been "in turmoil".
Obviously this overlaps with the criticisms over the Clinton emails, but Mr Trump's language has been broader and more sweeping.
This appeared to contradict White House claims that Mr Trump acted on the deputy attorney general's recommendation.
On Wednesday, he tweeted that Mr Comey had "lost the confidence of almost everyone in Washington, Republican and Democrat alike. When things calm down, they will be thanking me!".
Mr Trump tweeted that Mr Comey had "lost the confidence of almost everyone in Washington".
The same day, Ms Sanders and Vice-President Mike Pence said Mr Trump had fired Mr Comey on Mr Rosenstein's recommendation - which was mainly related to Mr Comey's handling of the Clinton emails probe.
But Mr Comey's successor, acting FBI Director Andrew McCabe, told the Senate "the vast majority of employees enjoyed a deep and positive connection to Director Comey".
But on Thursday, Mr Trump told NBC he had already decided to fire Mr Comey, "regardless of recommendation".
And Ms Sanders said he had been considering firing Mr Comey since he was elected in November, as there had been "an erosion of confidence" over the past year.
It's also notable that Mr Trump has not been entirely opposed to the way the emails investigation was handled.
Although he was highly critical when Mr Comey said the investigation into Hillary Clinton's emails would be closed without prosecution last July, he later praised the FBI chief for reopening it less than a fortnight before the presidential election, saying the move "took guts".
Also controversial is Ms Huckabee Sanders's statement at a briefing on Wednesday that "the rank and file of the FBI had lost confidence in their director".
Mr Comey's successor, acting FBI Director Andrew McCabe, pushed back against this on Thursday, telling the Senate intelligence committee that "that the vast majority of employees enjoyed a deep and positive connection to Director Comey".
The committee's chairman, Republican Senator Richard Burr also painted a contrasting picture, describing Mr Comey as "one of the most ethical, upright, straightforward individuals I've had the opportunity to work with."
"Sure there were FBI employees that disagreed with how he handled the Clinton email announcements," Mr Burr said. "The lion's share of FBI employees respect the former director and it shows the professionalism that he brought to the role that he was in," he he was quoted by NBC News as saying.
3) Russia
3) Russia
Democrats have been quick to assert that Mr Comey's role leading the FBI investigation into alleged Russian meddling in the election - and possible Russian links to the Trump campaign - was the real reason for the sudden dismissal.
Democrats assert that Mr Comey's role leading the FBI investigation into alleged Russian meddling in the election - and possible Kremlin links to the Trump campaign - was the real reason for his abrupt dismissal.
Mr Comey confirmed that such an investigation existed only on 20 March, when he spoke before a congressional intelligence committee.
Mr Comey confirmed that such an investigation existed on 20 March, when he spoke before a congressional intelligence committee.
Nothing has come from this investigation yet; Mr Comey said it was "very complex" and that he could not give a timetable for its completion.
After his dismissal, Politico reported the president "had grown enraged by the Russia investigation" and was "frustrated by his inability to control the mushrooming narrative".
But US intelligence agencies concluded in a January report that Russian President Vladimir Putin did order the hack against the DNC. And the Russia scandal has already claimed one Trump official - former national security adviser Mike Flynn, who was fired for not giving a correct account of his meetings with a Russian official.
The White House has consistently denied having links with Russia. But after Mr Comey's dismissal, Politico reported that the president "had grown enraged by the Russia investigation" and was "frustrated by his inability to control the mushrooming narrative around Russia".
"He repeatedly asked aides why the Russia investigation wouldn't disappear and demanded they speak out for him," Politico reported. "He would sometimes scream at television clips about the probe, one adviser said."
"He repeatedly asked aides why the Russia investigation wouldn't disappear and demanded they speak out for him," Politico reported. "He would sometimes scream at television clips about the probe, one adviser said."
Mr Comey had been due to appear before the Senate intelligence committee to speak on Russia on Thursday. Senator Burr said he was "troubled by the timing and reasoning of Director Comey's termination".
Russia: The scandal Trump can't shake
Two senior Democrats have also told US media they understand that days before he was sacked, Mr Comey had sought more resources - including more staff - for the Russia investigation.
President Trump did say in his NBC interview that he was bearing in mind "this Russia thing" in his decision, describing it as a "made-up story" and an "excuse" by the Democrats for their election loss.
He said he had noted that the sacking might have an impact on the investigation, by lengthening it, but said he had to "do the right thing for the American people".
He also said he wanted the investigation to be "absolutely done properly", despite saying in a tweet on Monday: "The Russia-Trump collusion story is a total hoax, when will this taxpayer funded charade end?"
4) He was a 'showboat'
4) He was a 'showboat'
"He's become more famous than me!" Mr Trump said when beckoning Mr Comey at a January meeting, sending an air-kiss his way.
"He's become more famous than me!" Mr Trump said of Mr Comey at a January meeting, sending an air-kiss his way.
But could this have been a problem, rather than a compliment?
But could this have been a problem, rather than a compliment?
In his NBC interview, the US president described Mr Comey as "a showboat, a grandstander".
In his NBC interview, the US president described Mr Comey as a "showboat" and "grandstander".
Citing unnamed White House officials on Wednesday, the Wall Street Journal reported the two were a poor match, and that Mr Trump did not like the increased media attention on Mr Comey.
Citing unnamed White House officials, the Wall Street Journal reported that Mr Trump chafed at the increased media attention on Mr Comey.
"He viewed Mr Comey as eager to step in front of TV cameras and questioned whether his expanding media profile was warping his view of the Russia investigation," the officials said, according to the report.
"He viewed Mr Comey as eager to step in front of TV cameras and questioned whether his expanding media profile was warping his view of the Russia investigation," the officials said, according to the report.
5) Loyalty
5) Loyalty
Loyalty is one Mr Trump's most prized qualities - and according to the New York Times, two of Mr Comey's associates say he refused to promise it.
Loyalty is one Mr Trump's most prized qualities - and according to the New York Times, two of Mr Comey's associates say he declined to pledge it.
Over dinner in January, the president asked the FBI head whether he would pledge his loyalty, and Mr Comey said he would always be honest, but that he was not "reliable" in the conventional political sense, according to accounts reported by the paper.
Over dinner in January, the president asked the FBI head whether he could count on his loyalty, but Mr Comey only promised to be honest, according to the newspaper.
Separately, Mr Trump is also reported to have been furious that Mr Comey publicly dismissed his sensational claim in March that President Barack Obama had wiretapped him and annoyed by what appeared to be a lack of motivation to investigate leaks that hurt the White House - perhaps also seen as a lack of loyalty.
Mr Trump is also reported to have been furious that Mr Comey publicly dismissed his sensational claim in March that President Barack Obama had wiretapped him.
After Mr Comey testified to a Senate committee about the Russia and Clinton email investigations last week, including saying he was "mildly nauseous" to think that his handling of the Clinton case might have swayed the election, Mr Trump began seriously considering firing him, the New York Times reports.
After Mr Comey testified to a Senate panel on 3 May that he felt "mildly nauseous" to think he might have swayed the election, Mr Trump began seriously considering firing him, the New York Times reports.
Is Trump's thin skin to blame?
Is Trump's thin skin to blame?
6) Something in between, a mixture, or none of the above
Only one person knows for sure: the president of the United States.
