Sir Alex Ferguson is retiring as manager of Manchester United, the club has confirmed.
The manager, who has been at the club for 26 years, said in a statement: "The decision to retire is one that I have thought a great deal about and one that I have not taken lightly. It is the right time.
"It was important to me to leave an organisation in the strongest possible shape, and I believe I have done so."
The Scotsman secured his 13th Premier League title with Manchester United two weeks ago and is the most successful manager in British football history.
An announcement is expected within days, with Sky sources saying Everton boss David Moyes is in "pole position" to get the job.
Ferguson, 71, will stay at Manchester United as a director and an ambassador, but now has just two games left with the famous club.
His final game, away to West Brom on May 19, will be his 1,500th in charge.
"With these activities, along with my many other interests, I am looking forward to the future," said Ferguson.
"I must pay tribute to my family, their love and support has been essential."
The success of the club would continue without him, said Ferguson, who had a stand at Old Trafford named in his honour in 2011.
"The quality of this league winning squad, and the balance of ages within it, bodes well for continued success at the highest level ... the long-term future of the club remains a bright one," said Ferguson.
Premier League chief executive Richard Scudamore told Sky News the Scot was a "constant professional" who was bowing out on a high.
"In some ways it's a shock, in some ways the timing couldn't be better," he said.
FA chairman David Bernstein hailed Sir Alex's tenure as "truly remarkable".
"He is genuinely one of the greatest managers of all time and certainly of the modern era. His contribution to English football has been outstanding in every regard," said Mr Bernstein.
The Prime Minister, David Cameron, also joined in the tributes and tweeted: "Sir Alex Ferguson’s achievement at #MUFC has been exceptional. Hopefully his retirement will make life a little easier for my team #AVFC".
The "foundations of the Premiership have shaken this morning", said Sky News Sports Correspondent Paul Kelso.
"Fergie steps aside as the greatest figure in football management - there’ll be a very long queue of managers seeking to replace him."
Old Trafford bosses may be wary of bringing in a "restless manager" like Jose Mourinho, said Kelso - despite his impressive track record.
A manager like David Moyes, who is seen to have "over-achieved" at Everton, is looking like the more likely choice.
"Crucially, if he (Moyes) has Sir Alex Ferguson's blessing, it will buy him time with the fans to prove he's a worthy successor," said Kelso.
Former and current players have also been praising Sir Alex's achievements and having their say on who should fill his boots.
"You have to be a certain manager to manage Manchester United," former United player Paul Ince told Sky News.
"It's very important the next man is the right man."
Michael Owen, who is himself retiring at the end of the season, tweeted: "What an act to follow. I guess only Mourinho would have the confidence to strut through the door. If it were me, I'd go for Moyes."
But former United keeper Peter Schmeichel said Sir Alex should have stayed on a bit longer.
"(I'm) shocked, disappointed and very sad," he told Sky News. "I was hoping it was a couple of years down the line."
The Danish player, who was with the club for most of the 90s, said Ferguson was an inspirational leader who always had time for him, and the best manager the game had ever seen.
Cristiano Ronaldo simply tweeted a picture of himself with the manager, along with the words: "Thanks for everything, Boss."
The announcement, which comes just a day after back page speculation, will be a cause of concern for Manchester United investors. It means there will soon be a new chief executive and manager in place at Old Trafford.
When David Gill confirmed he would quit as CEO in June, it sparked a deterioration in the club’s share price.
Sir Alex, who began his managerial career in Scotland in 1974, enjoyed success with St Mirren and Aberdeen before moving to England.
He won 49 trophies during his career - his haul with Manchester United including five FA Cups, four league cups and two famous Champions League titles, in 1999 and 2008.
However, the manager's quest for a coveted third European title ended this season with a 3-2 aggregate loss to Real Madrid.