Reaction to Wednesday's announcement by Premier League champions Manchester United that manager Alex Ferguson will retire at the end of the season:
David Gill, Manchester United chief executive, in a statement: "We knew that his retirement would come one day and we both have been planning for it by ensuring the quality of the squad and club structures are in first-class condition. What he has done for this club and for the game in general will never be forgotten. It has been the greatest experience of my working life being alongside Alex and a great honor to be able to call him a friend."
Joel Glazer, Manchester United co-owner, in a statement: "Alex has proven time and time again what a fantastic manager he is but he's also a wonderful person. His determination to succeed and dedication to the club have been truly remarkable. I will always cherish the wonderful memories he has given us, like that magical night in Moscow (in the 2008 Champions League final win)."
Sepp Blatter, FIFA president, on Twitter: "His achievements in the game place him without doubt as one of the greats. Was (an) honor to present Sir Alex with award at 2011 Ballon D'Or. Will his longevity at the top ever be repeated?"
Michel Platini, UEFA president, on uefa.com website: "Sir Alex has made a massive contribution to football, not only in Scotland and in England but across Europe and beyond.
His dedication, his attention to detail and his unique eye for talent, as both the manager of Manchester United FC and Aberdeen FC, has brought rich rewards over a 30-year period. His CV is almost unique in a results-based profession that normally focuses on short-term solutions rather than long-term vision.
"He is a true visionary and I hope that, having helped us in the past through various coaching initiatives, he will continue to collaborate with UEFA to share his fantastic knowledge with the next generation of up-and-coming European coaches who all wish to emulate his achievements in the sport."
Roy Hodgson, England manager, in a statement: "The unexpected news this morning that Sir Alex Ferguson has decided to retire marks the end of an era in football management. No one will be able to match his achievements, his dedication, his support for colleagues in need and his team building know-how. This is a sad day for English football. I personally wish him a happy and successful retirement."
Richard Scudamore, Premier League chief executive, on Sky Sports News: "You know it's one of those things you know is going to happen one day but you never really expect it to happen. It's a big shock. (The Premier League's) absolute leading club and its standard-bearing club has been Manchester United... nobody has been a bigger star on our stage than Sir Alex Ferguson... It's an unbelievable footprint he's made on the Premier League."
Gordon Taylor, chairman of the Professional Footballers' Association (PFA), to local media: "The game of football will be a lot poorer place without him. He has been quite simply the best. He followed in Sir Matt Busby's footsteps and even surpassed him. He will also be the toughest act to follow. I will miss him - he has been a very good friend of the PFA throughout his career. Of course, at times it has not always been smooth and we have had a difference of opinion but we always respected each other and we have had a lot more agreements than disagreements."
David Bernstein, chairman of the Football Association, on the fa.com website: "Sir Alex Ferguson's achievements are 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 and, in the FA's 150th year, it is something that should be celebrated. On behalf of the FA I'd like to wish him a happy and healthy retirement."
Howard Wilkinson, chairman of the League Managers Association, in a statement: "Today's news draws to a close the career of a man and a manager, the likes of which we will never see again. His public face was always that of the ultimate professional with a fierce pride and determination to do the very best for his club... He is the epitome of the mantra 'Survive, Win, Succeed'. But, in private, with those he trusted, he was the very best sort of friend you could ever wish for."
Cristiano Ronaldo, Real Madrid and Portugal forward and former Manchester United player, on Twitter: "Thanks for everything, Boss."
Paul Ince, former Manchester United player, to Sky Sports News: "The man was immense. I'm totally shocked. What he's done is unbelievable. You'll never see anyone of his kind again. Two weeks ago he was talking about staying on for another two years, so it's a massive, massive shock. The way he treated me was like a son."
Dwight Yorke, former Manchester United player, to Sky Sports News: "He took the footballing world by surprise in retiring. With his hip replacement, and with David Gill going as well, that probably pushed him a bit into thinking he was going to retire. He wanted to regain the Premiership this year; he's done it. In many respects it's probably the right time to go. It will take some getting used to."
Duncan Drasdo, chief executive of Manchester United Supporters' Trust, in a statement: "Like United fans all over the world we will be sad to see Sir Alex go. Simply he is a one-off and irreplaceable. Our first reaction is an overwhelming feeling of immense gratitude towards Sir Alex for the truly outstanding contribution he has made to our football club. We are sure his influence will continue to be felt directly at Old Trafford, in the dressing room and in the stands, for some time to come and his legacy will last forever."
Ole Gunnar Solskjaer, former Manchester United striker and the club's former reserve team coach, on Norwegian television: "What he has done at United is completely unique. I'm incredibly proud to have been a part of it, both as a player and a coach. I'm completely certain they've found their man (to succeed Ferguson), and I think I know who it is. The club faces a great challenge in finding the right man, but I'm sure they have done so."
Clayton Blackmore, former Manchester United player, to BBC Radio 5 Live: "It comes with a heavy heart. We have heard the rumors and the papers speculating, and I didn't want to believe it as he has done such a fantastic job and we wanted to keep him there. He deserves his time to sit back and enjoy what he has done. It is going to be emotional on Sunday. I'm sure the manager knows who will replace him and he will have his say. It would not surprise me if David Moyes takes over."
Bryan Robson, former Manchester United captain, to Sky Sports News: "It doesn't become a real shock as he had considered it before, I just think with winning the title and getting it back from City this year, I think maybe it (was time to spend) time with his grandchildren, the timing is right. You've got to say he has been the greatest club manager there's ever been anywhere in the world."
Denis Law, former Manchester United striker, on Sky Sports News: "He will probably... be the greatest manager ever but he's in that category of great managers... He has created, like (Matt) Busby did many years ago the Busby Babes, young players coming into the team all together... he has created, like Busby did, three or four great teams in his spell as manager.
"When I heard Alex had retired I couldn't believe it. I was with him last week and there didn't seem anything at all (to suggest it might happen now).
Bobby Charlton, former Manchester United player and current club director, quoted by local media: "He is such a fantastic manager... He is a sensational person in every form and I am really delighted for him. I am a director but I hardly do anything because we are winning all the time and it is all down to Sir Alex Ferguson.
"He would get up in the middle of the night and travel 300 miles if he thought there was a schoolboy that he could sign. He loves the game and we at the club have had nothing to do really."
Vincent Kompany, Manchester City captain, on Twitter: "Sir Alex, one of the best managers of all time. After 26 years of success in the game, we all owe him a tribute."
Michael Owen, former Manchester United striker, on Twitter: "It's just not sinking in! Manchester United with no Sir Alex just doesn't feel right. What a man and great that it has ended on his terms... his record will surely never be eclipsed."
Peter Schmeichel, former Manchester United goalkeeper, to Sky Sports News: "I can't make sense of the timing. It has come as an absolute bombshell. I'm disappointed and shocked."
Edwin van der Sar, former Manchester United goalkeeper, on Twitter: "Was coming for some time now but still a shock that hasn't sunk in yet!! Great manager and remarkable person!"
Dennis Irwin, former Manchester United player, to MUTV: "It's a sad day for Manchester United. It's a day we should celebrate what he's done for Manchester United. It was always going to come as a shock. Without doubt the best manager that's ever lived."
Sergio Busquets, Barcelona and Spain midfielder, at a news conference: "An historic coach is leaving us, a coach who will always be remembered in the world of football. It's a loss both for United and for the football world. The career he has had is spectacular, with everything he has won. He is an example for clubs who want a coach to stay on for so many years, always able to compete and be among the best. I want to congratulate him on his career. He will be missed for sure."
Radamel Falcao, Atletico Madrid striker, on Twitter: "Stand up, put your hands together and give him a big round of applause! Sir Alex Ferguson is retiring. Congrats for an amazing career!"
David Gold, chairman of West Ham United, on Twitter: "Sir Alex, why are you retiring? I could understand it if you were old. Good luck in your future endeavors."
David Cameron, British Prime Minister, on Twitter: "Sir Alex Ferguson's achievement at #MUFC has been exceptional. Hopefully his retirement will make life a little easier for my team #AVFC (Aston Villa)."
Patrick Vieira, former Arsenal and Manchester City player, on Twitter: "It is the end of an era for a truly great ambassador, not only for the Premier League but for football overall. Best of luck to Sir Alex."
Steve Bruce, Hull City manager and former Manchester United defender, to Sky Sports News: "We're shocked, nobody saw it coming. He's obviously been thinking about it for a long, long time. He will be a big hole to replace. It wouldn't surprise me if it's David (Moyes as next manager) and we wish him well. Whoever takes over... he's going to be some act to follow. It doesn't seem quite right that Fergie won't be in charge any more. I don't think the next manager will do 27 years."
Ron Atkinson, Ferguson's predecessor at United, on MUTV: "The significant thing might be the 20th (league title). I honestly didn't think he would finish, I thought he'd have at least another two years at it, maybe try to nick the European Cup back."
Avram Grant, former Chelsea manager, on Sky Sports News: "It was a shock. Alex always looked very passionate about football, especially in the last year, more than any other year. He looked like he would be forever at Man United. You never know what's happening in the head of a person until you know their decision."