Simon Grayson has been sacked after just 18 games as Sunderland manager, with the team 22nd in the Championship.
His departure, announced 17 minutes after a 3-3 draw with bottom-of-the-table Bolton Wanderers, comes just four months after he was appointed.
The former Preston North End boss took over at the Stadium of Light in June, replacing David Moyes, who left after the club were relegated.
However, the 47-year-old won just one league game as Sunderland boss.
Assistant manager Glynn Snodin has also gone, with no announcement as to who will take caretaker charge of the team for Sunday's Tees-Wear derby against Middlesbrough.
Chief executive Martin Bain said: "Simon and his team have worked tirelessly to achieve the best for the football club during their time here.
"While we hoped that Simon's experience in the Football League would help us to a successful season, results have not been good enough for a club of this stature.
"In order for us to improve upon our current position we believe a fundamental change is necessary."
Grayson had stated his confidence that he was the "right man for the job" as recently as Monday's media conference to preview the Bolton match, despite the pressure surrounding the game.
"Am I the right man? Certainly am," he told BBC Newcastle. "I've been through things. There aren't better or experienced managers out there that would want this job, or can do a better job than what I'm doing at the moment in time."
But Tuesday's failure to beat the division's bottom side, thus continuing a winless home run that goes back to December 2016, marked the end of Grayson's short reign.
He is the ninth permanent manager to depart the Wearsiders since Roy Keane's exit in December 2008.
'Who is going to pick Sunderland up?'
Stoke City and Scotland midfielder Charlie Adam told BBC Radio 5 live: "The players on the bench are the players who have played in the Premier League and they can't get in the team.
"I have played against a lot of these players and the confidence is low. Who is going to pick Sunderland up?
"I fear for the club."
Former England defender Phil Neville: "I wonder whether it can get any lower than it is at the moment. The training ground is as good as any Premier League club.
"Historically, they have one of the best clubs so I don't think it's as bad a job as people are making out.
"All of the previous managers have got vast experience and they have all had the same problems.
"It needs somebody to go in there, grab those young players, be a little bit aggressive and give them something.
"The place needs lifting. There is no positivity. I think it is an attractive proposition. There are British coaches in the lower leagues who would jump at the opportunity to manage Sunderland."