Is Ferguson the greatest ever?
Sir Alex Ferguson's lasting legacy to Manchester United cannot be accurately measured until the day he retires - but one simple truth is already beyond dispute as he celebrates his 25th anniversary at the club.
Ferguson may be a divisive figure to some without a strong allegiance to Old Trafford, but even those who temper their admiration for the Scot cannot contest his right to be regarded among the finest managers football has known.
When the list of great managers is compiled, Ferguson's name will be near the top of some lists and at the top of others, alongside the founding father of United, Sir Matt Busby, Liverpool's Bill Shankly and Bob Paisley, the maverick Brian Clough at Derby and Nottingham Forest and his own inspiration, former Celtic and Scotland manager Jock Stein.
Tottenham fans will make a case for double-winner Bill Nicholson and Leeds United fans revere Don Revie while Ferguson's long-time adversary Arsene Wenger's early successes put his indelible stamp on Arsenal.
Former England manager Graham Taylor was a Division One rival of Ferguson's at Watford when he arrived from Aberdeen in November 1986 - and he has no hesitation when asked where he ranks Ferguson.
He told BBC Sport: "I think he is the all-time great manager. You can't compare his era to another you can only contrast it, because the comparisons are not fair. There are so many other different things to take into consideration.
"But if you look at those other eras and contrast them and see what each manager has done then I think he is the number one. He has proved to be the best manager in the history of football."
Victory in the 1999 Champions League final against Bayern Munich to secure the Treble is probably Ferguson's greatest achievement. Photo: Getty
Former Liverpool captain Alan Hansen won three European Cups, two under Paisley, and is understandably more guarded about where he places Ferguson in the managerial order of merit.
He said: "Of course people will want to compare Alex with the great manager I played under at Liverpool, Bob Paisley. It is so hard to make those comparisons and everyone will have a different opinion shaped by their own experiences and even the club they support, but it is safe to say they were and are both magnificent servants to Liverpool and Manchester United - iconic figures at their clubs.
"Bob won the Uefa Cup in 1976 when it was not ranked too far behind the European Cup, then he won the European Cup in 1977, 1978 and 1981. Four huge European trophies in five years while picking up league titles as well.
"Alex's record in the League and FA Cup is phenomenal and he has taken Manchester United to four Champions League finals, winning two and, also winning the Cup Winners' Cup with both Aberdeen and United - a brilliant and prolonged track record of success. You can argue the merits but both have the record of sustained success to be regarded as magnificent managers."
Walter Smith, Ferguson's long-time friend from Glasgow and assistant with Scotland at the 1986 World Cup and for a brief spell at United in 2004, told BBC Sport: "I don't think there is any doubt that Alex will go down as one of the greatest managers there has ever been.
"As a manager he has a fantastic instinct for what is right, whether it is tactics, team selection or changing things when a game is going on. When you work with him you realise this, and this is part of what has made him so successful."
What separates Ferguson from the other managers on that illustrious roll of honour is the scale of his success at Manchester United over such a lengthy period, from his appointment 25 years ago through his first success with the FA Cup in 1990 and their current status as record 19-time League champions.
Ferguson has nurtured many players from the youth academy, including the class of 92. Photo: Getty
Taylor said: "To reach a landmark of 25 years at one club is the result of tremendous perserverance and a complete belief that what you are doing is right. Criticism from certain people may upset him because he might not regard them as football experts but he will listen and take things on board - he will have to because the game has undergone so many changes in the last 25 years.
"He must be very highly motivated and have a real drive. Alex himself will probably admit that one of his few mistakes was when he announced his retirement. He pulled out of that but at the time he was probably just a bit tired, which is perfectly understandable.
"Alex will have learned to delegate a lot more. Clubs, certainly clubs like Manchester United, are too big for even someone like Alex to be in charge of every department, but for the important final decisions it will come back to him.
"One of his greatest assets has been to move with the times in football. With the formation of the Premier League, the more intensive coverage, and the number of games in the Champions League, you really have to be on the ball and you learn that art of delegation over day-to-day matters.
"This will have been so important and his selection of people to work with has been very good. He is able to let them get on with their jobs but when it is a major football decision it all comes back to him.
"People ask how a man approaching his 70th birthday and after 25 years at Manchester United can still find a way to drive himself on every morning - being successful helps for a start but he must also have great strength of character. In that respect Alex is pretty much unique.
"Once he won the FA Cup in 1990 and the European Cup Winners' Cup against Barcelona the following year he was on his way. He has maintained that success level ever since and not too many years pass by without Manchester United winning something.
"I think it is difficult to see anybody ever repeating his length of time at one club in this day and age, in fact I would say it is nigh on impossible."
The old football adage of "show us your medals" is often used to measure a man's standing in the game.
Taylor's response is simple: "If anyone ever wants to put that to the test with Alex, it would need a very big table to accommodate those medals."