Great Scot.

Perhaps made most famous (phonetically, at least) in a much-loved film about time travel (and the potentially tricky situation of seducing one of your parents), the exclamation is surely apt in these first few hours after an announcement that has brought about anything from shock to scorn, damnation to dismay, gratitude to glee.

Sir Alex Ferguson has announced his retirement.

Not like you haven't heard, of course. Trending on Twitter, dominating Facebook, and I'm sure there are already a bunch of tribute Instagram compilations (accounts?) bearing names like "Fergie26" or "SAF_ROX". The real issue of course, is not that it happened - it isn't even the first time it has - but that it happened so suddenly, and that it opens up a whole new world of opportunity and uncertainty.

A former colleague of mine, Liverpudlian true and true, once said that Sir Alex Ferguson was an institution, and that he, more than anyone else, represented a dynasty. That he individually has won more League titles than Arsenal as a club speaks volumes of his drive and motivation (the "cocker spaniel" Ryan Giggs shared this stat as well), and as the manager with the second-highest win ratio in the Premier League, his ability - either tactical adeptness or his motivational talents - cannot be questioned. One has to remember as well that the wily old Scot has repeatedly been met with criticisms of his many sides, usually along the lines of them being "a weak Manchester United squad" and still managed to match or best nearly all before him without splurging. The rather insightful stat from a prominent UK-based newspaper has revealed that Manchester United have spent less on transfers in their entire Premier League history than Manchester City have in the last five years.

But it is not the tributes to the departing Ferguson that has left mouths watering, eyes glued to smartphones and fingers rapidly mashing F5. It is that uncertainty. The question of who will follow in his hallowed footsteps? Who has the ability, the gall, the charisma to take charge now of Old Trafford?

Let's see.

David Moyes
One of the leading candidates, and the pundits preferred pick in many instances. A fellow Scot that has always been respectful and full of praise for Ferguson and United, he's the third-longest serving manager in the Premier League, which in itself suggests an ability to bring about stability (more on the second-longest later). In Wayne Rooney, Ross Barkley, Seamus Coleman, and other starlets, Moyes has also demonstrated a belief in developing youth, which is reported to be important to the United board. Much-lauded for his decade at Everton, some criticize his lack of trophies with the Merseyside club, but you have to consider that he's turned them from the jealous, workman-like, ungainly neighbours of Liverpool to a team that has flying wingbacks and one of the most potent attacking midfields in the League. If he chooses to.

And therein lies the problem. It seems to go against the philosophy of Manchester United to appoint someone who can sometimes come across as unambitious on the pitch (he discarded his attacking 442 in the recent Merseyside stalemate), though conversely, he's also been able to consistently trouble United in recent meetings, save the latest 2-0 loss where Gary Neville pounced on his brother's individual mistakes.

He has worked with a number of former United players though...

Jurgen Klopp
Another name much-touted my many. The man has done magnificently at Borussia Dortmund, winning the Bundesliga in 2010/11 and 2011/12 despite spending much less than Bayern Munich. This season, his side are well off the pace of the Bavarians in the league, though they are well ahead of Bayer Leverkusen in third as well. He has, of course, led Dortmund to the Champions League final, facing Real Madrid four times and Manchester City twice.

An advocate of attractive, attacking football, that particular trait may suggest a good fit at Old Trafford, though one wonders why he would leave such a brilliantly-run club that has enjoyed so much success. The potential answer to that, of course, is that next season may prove to be a formality; Bayern Munich, already with a massive advantage, have splashed the cash to activate Mario Gotze's release clause, "stealing" Klopp's crown jewel, albeit for 37 million Euros. This is yet another loss of a key midfield playmaker for the club and for Klopp, after Nuri Sahin and Shinji Kagawa left in recent times.

Wait a minute, Klopp and Kagawa? With Lewandowski leaving as well? Hmm.

Frank de Boer
A "left field" option according to another one of my colleagues, and an intriguing one. The legendary defender who once played in the same side as Pep Guardiola has done magnificently at Ajax Amsterdam, and they recently lifted their third straight Eredivisie title. To win a league as tight as the Dutch one is no mean feat, especially considering that few Dutch clubs ever spend greatly, and it is probably the most competitive top-flight league in Europe. The Ajax side is legendary in its youth development, of course, having produced and/or nurtured countless stars in the past two decades, and De Boer himself was the manager of the Ajax youth side before taking the step up. The winning mentality and focus on youth will lend much credibility to a man who many haven't even thought of.

And he's a twin, and twins are always cool. Maybe he can turn Rafael and Fabio into legends.

Arsene Wenger
The age-old nemesis, and the longest-serving manager in the league after Sir Alex. Wenger is also the one, (naturally) behind Ferguson with the most number of BPL wins under his belt, though that's still 161 less than the Scotsman. Someone who has always emphasized bringing in and utilizing young players, that meets the requirements that have apparently been set by the United board.

But here's the clincher.

It seems like Arsene Wenger has long abandoned his winning mentality. The Wenger of old, the one that commanded two truly fantastic sides, seems long gone. Now it seems he is more than content with a top-four finish and kicking bottles of water around the dugout. Some might argue that he is doing the best he can with what he is given, but isn't David Moyes then doing even better?

But there's the RVP connection...

Mike Phelan
Ferguson's assistant, less talkative that Carlos Queiroz or Steve McLaren, he hasn't been tested, though has taken charge of a few United games when Ferguson has been ill, or been scouting players and sides. Comfortable working with and under Ferguson, for sure, but as we've seen with Jordi Roura (and Carlos Queiroz), it is sometimes a step too far.

Ole Gunnar Solskjaer
One of a number of former United players who gone into management, the Baby-Faced Assassin is one of the few of those who have tasted success, though that's in Scandinavia with Molde. That being said, however, he also successfully managed the Manchester United reserves, winning several competitions with the second (or third or fourth) stringers. Winning with United is in his blood. Also once offered the job to manage Norway, so can't be too bad.

Despite that, and the heroics and goalscoring exploits that will always be associated with the man who has a banner stating his legendary status, it will be hard to see him coming in as anything but an understudy. The same can be said from anyone from Gary Neville to Ryan Giggs, Roy Keane to Eric Cantona. 

Jose Mourinho
This is the one you've all been waiting for.

The Special One is the only one to better Ferguson's win ratio in the Premier League, and at 70% nobody else comes close. He's won trophies everywhere he's been, shocking Manchester United and controversially knocking them out en route to winning the Champions League a season after winning the Europa League, before moving to Chelsea and dominating the BPL, and Ferguson, in his stint at Stamford Bridge. The San Siro was next, where he turned a good Inter Milan side into a truly great one, again winning the Champions League and securing a famous treble (like Ferguson). Then on to Real, his most controversial job yet in a career defined by controversy. 

He dropped a mainstay of the first team, a fan favourite and regular starter for the national side, got into heated arguments with key members of the squad, assaulted others, made headlines in the press, and scored a bunch of goals along the way. Now substitute (no pun intended) Iker Casillas for any one of Wayne Rooney, Ruud van Nistelrooy or Paul Ince, and do the same for Sergio Ramos and Pepe for David Beckham and Roy Keane.

He has, of course, broken Barcelona's invincibility, even before Bayern did, though this season has been punctuated by discord and strife and the backroom politics of the Bernabeau.

But it that turmoil that will count against him, surely. Sir Bobby Charlton has already come out to say he doesn't approve of Mourinho's antics, though it may well be a clever double bluff. Silvio Berlusconi called Mario Balotelli a "rotten apple", after all, and now he's the toast of the Rossoneri.

But Mourinho is Chelsea-bound, right?

Well... Let's revert back to the first pop-culture reference I used. Enter your DeLorean and hit 88, go back to when Wayne Rooney wanted to leave Manchester United.

"He belongs to Manchester United."

When I first heard that, I turned jokingly to a colleague and said "that's because Jose is coming to United and wants to manage Rooney!" Mourinho was later the VIP at the LMA Awards Dinner, and was asked on camera about a return to the BPL, where he maintained that he definitely would like to (as he has several times), but he also stated he didn't have to go to a London club.

Well, well, well.

Interesting to note, especially with him being pictured buying boxes from IKEA recently, but will he pick red over blue? Is Jose Mourinho and his 20 million Euro release clause the "big signing" that Ferguson himself promised?

His motivation is unquestionable. He wants to win, and win at all costs. He has won almost everything everywhere he's been. Each stop in his managerial career has seen a trophy cabinet bulge. 

But that's the thing.

There is no stability, no lasting legacy, no dynasty. Along with some silverware, Mourinho also leaves behind destruction in his wake. An overworked squad - Rafa Benitez had to deal with more than 10 senior players injured his entire time at Inter - jaded from the rigours of Mourinho's system, the lasting cliques and politics - AVB and those before him had to deal with the Lampard/Terry/Drogba coalition - that future managers struggle with, a depleted and ignored youth system and, of course, how every side he has left has then gone on a mad manager spree after. One may argue, of course, they have just been spoilt, and that no-one can match his work and so are viewed as lessers, but the counter-argument is equally poignant.

He leaves his successors nothing to be successful with.

And taking that point, cutting it down like Occam, we have,

"He leaves."

After 26 years of building greatness, is this what United crave?

We'll find out soon enough.