Legendary coach Bill Belichick says his success "exceeded his wildest dreams" as he confirmed his exit from the New England Patriots after 24 years.
Belichick has agreed to leave after another poor season in which the Patriots came last in the AFC East for the first time since 2000.
But, alongside quarterback Tom Brady, Belichick won a record six Super Bowls with the franchise from 2001 to 2018.
"For me, this is a day of gratitude and celebration," said the 71-year-old.
The Patriots were also runners-up three times under Belichick's leadership and he added: "We had a vision of building a winner, a championship football team, here and it exceeded my wildest dreams and expectations.
"I will always have those great memories and will carry those for the rest of my life."
Belichick's six Super Bowl titles are a record for a head coach and his departure was confirmed after discussions with franchise owner Robert Kraft.
At a short news conference, Kraft said: "The man standing to my left brought the leadership and coaching skills that were needed to make this unprecedented success possible.
"He is the greatest coach of all time, which makes this decision to part ways so hard.
"This is a move we mutually agreed was needed at this time. What Bill achieved with us will never be replicated."
Despite the previous success, Belichick's Patriots have only made the play-offs once since Brady left in 2020.
They ended the latest regular season on Sunday with defeat by the New York Jets. It was their 13th loss of the campaign, the most Belichick has endured during a season in his 26-year head coaching career.
On Sunday he said it was "way too early" to decide his future, having reportedly signed a multi-year deal at the start of the 2023 season.
Belichick's Patriots have finished with losing records in three of the past four seasons. The team recorded back-to-back losing campaigns for the first time since 1993 this term.
During their golden period, led by Brady and Belichick, they played in nine Super Bowls - more than any other NFL franchise.
They also won 17 division titles, made 13 AFC championship game appearances and had the only undefeated 16-game regular season in 2007.
Belichick has eight Super Bowl titles in total after winning two titles as defensive coordinator of the New York Giants. He was also runner-up during a short spell as Patriots assistant in 1996.
He is the head coach with the most play-off appearances (19), play-off games (44) and play-off wins (31) and, with 333 victories overall - including play-offs - is second on the all-time list behind legendary Miami Dolphins coach Don Shula on 347.
Belichick will turn 72 in April and has been coaching in the NFL since 1975 but, with Shula's record in sight, it has been reported in US media, external he wants to stay in the league.
The Los Angeles Chargers, Arizona Cardinals and Washington Commanders have all been linked with the three-time NFL coach of the year.
Analysis
During the Patriots' golden era, there was always a debate over whether their success was more down to Brady or Belichick.
Some dismissed Brady as a 'system quarterback', yet the fact he went on to win a Super Bowl in his first season away from New England - with an unfancied team such as the Tampa Bay Buccaneers - suggests he deserves more credit than he had been given.
Belichick, meanwhile, has been unable to replace him. Cam Newton lasted one season, while draft picks Mac Jones and Bailey Zappe have failed to hit the lofty standards Brady set, although the quality of the Patriots roster has gradually declined since he left.
As the team's de facto general manager, Belichick has been in charge of player recruitment as well as coaching. After winning three Super Bowls between 2001 and 2004, he managed to rebuild his team to win three more between 2014 and 2018.
Patriots owner Kraft has accepted he won't be able to regenerate his roster again, but just as Brady is now regarded as the greatest quarterback of all-time, Belichick is arguably the coaching GOAT for leading a franchise to such prolonged success in a sport where so much is in place to prevent it.
