There will never be another Sir Alex Ferguson, and it is a remarkable achievement that on Sunday he celebrates his 25th anniversary at the helm of Manchester United.
The million-dollar question is how long does he have left in charge at Old Trafford? I think he will continue for as long as he feels he can still communicate with the players and get the best out of them. Can he still command the players' respect? Can he still bring the club the success they deserve, year in, year out?
The moment he feels he is incapable of doing so he will step aside because he is not a selfish man. He is greedy, because he wants to win all the time, but he is not selfish. He knows that the time to go will either be determined by health reasons, or if his authority wanes. There has been little sign of that though.
It certainly doesn't appear as though his powers are in decline. He is still a formidable character; you can see when he clashes with rival managers or referees that the old fire is still burning strong. The only real change in Sir Alex since I played for him is his age. And that, as we know, is just a number.
He won't be going anywhere any time soon.
But when he finally does leave then Manchester United will probably panic, and rightly so. How do you replace a manager who is up there with, and possibly beyond, Bob Paisley, Bill Shankly and Sir Matt Busby in the history books?
Would United be able to go out and get someone who could bring them the same level of success that Fergie has guaranteed? I doubt it very much, and the law of averages suggests they won't.
I think this 25-year anniversary is something we are not going to see another manager emulate for a long, long time. Not unless Arsene Wenger can really turn things around at Arsenal.
And what has kept him at the top of the game for so long? An insatiable hunger to win trophies. You can't get success unless you are hungry for it, and that is what Sir Alex Ferguson is all about.
You need to be organised as well of course, because you can't last for a quarter of a decade at a club unless you are disciplined off the pitch. Sir Alex's excellence off the field has laid the foundation for so much success on it.
The game has changed a lot since Fergie first took charge in 1986 but he has gone with the changes and adapted every time. Many managers fight against change and their conservatism can be their downfall - they can be miserable old ex-pros who are disillusioned and disgruntled with what is going on in the game.
But every time the game has changed, Fergie has observed and then transformed the way he operates.
He has always ruled with an iron fist though, make no mistake about that. I played under Sir Alex for five years and one thing I would say is that you certainly knew where you stood. You didn't need a handbook to tell you the rules of playing for Manchester United: his manner and the way he led you told you all you needed to know. He instils something in you: a responsibility for behaving like a Manchester United player and a decent human being.
I felt the full force of the legendary hairdryer on occasions. Once I made the mistake of calling him 'Taggart', likening him to the fictional Scottish detective. Steve Bruce conned me into saying it. His reaction did make me question whether I was wise to say it and I certainly knew I would never say it again.
It went down very badly. I immediately panicked about whether I'd be around much longer, to be honest.
But he is not a man who bears grudges. That is one of the great things about him. If you do the job properly then you haven't got a problem. Players have always known where they stand with him, and where they stand with Manchester United Football Club.
I worked under some very good managers during my playing career, but Sir Alex was the best, there is no doubt about it. I played under Jim Smith at QPR, was fortunate enough to play for the late, great Sir Bobby Robson for England, but Sir Alex is the pick of the bunch.
I feel very proud to have been part of the Manchester United team that first established the club as a Premier League force and set Sir Alex on the way to winning all those league titles. It was great to be there for the start.
I can only judge on the managers I have seen in my lifetime, but Sir Alex is the only one who you could possibly consider as being the greatest. No one comes close to him. He is the best I have seen, beyond doubt.