Manchester United are one of the biggest and most successful clubs in the world, with several domestic and continental honours to their name. The club reached its peak under Sir Alex Ferguson, who was at the helm for 26 years. He guided the club to an unprecedented 13 Premier League titles.However, since his retirement in 2013, things have not always gone to plan at Old Trafford. Ferguson has left a huge legacy behind as Manchester United manager, one of the most coveted jobs in world football.NBC Sports Soccer@NBCSportsSoccerThe year was 2013, Sir Alex Ferguson's final season in charge of @ManUtd. We look back at the past decade and recognize a manager that truly changed the sport.3:30 AM · Dec 23, 201930960The year was 2013, Sir Alex Ferguson's final season in charge of @ManUtd. We look back at the past decade and recognize a manager that truly changed the sport. https://t.co/qlP3b6wUCSFerguson chose his successor - fellow Scot David Moyes - who was Everton manager at the time. However, under Moyes, Manchester United failed to defend their Premier League title and also missed out on European qualification for the first time since 1995-96. That led to Moyes' dismissal.Ryan Giggs was named caretaker manager, and then acted as assistant to Louis van Gaal between 2014 and 16. However, the Dutchman endured a sack following a poor run of results in 2016.Manchester United saw a glimpse of their past glory under Jose Mourinho, who won the Europa League in his first season in charge in 2016-17. That helped bring The Red Devils back to Europe's premier competition - the UEFA Champions League.However, Mourinho was sacked in 2018, with former Manchester United striker Ole Gunnar Solskjaer taking charge as caretaker manager. His 14 wins in his first 19 games in charge helped Solskjaer secure a three-year deal. However, he was relieved of his duties a few weeks ago after a nearly four-year-long trophyless run.Manchester United have since appointed Ralf Rangnick as their interim manager until the end of the season. He will take up a consultancy role for a further two years. The German is known for having mentored fellow Premier League managers Jurgen Klopp (Liverpool) and Thomas Tuchel (Chelsea). The former has especially heaped praise on Rangnick.Fabrizio Romano@FabrizioRomanoJurgen Klopp on Ralf Rangnick: “Unfortunately a good coach is coming to England, to Manchester United! He’s a really experienced manager, built two clubs from nowhere”. 🇩🇪 #MUFC“Man United will be organised on the pitch. That's obviously not good news for other teams”. #LFC6:06 AM · Nov 26, 20219782410380Jurgen Klopp on Ralf Rangnick: “Unfortunately a good coach is coming to England, to Manchester United! He’s a really experienced manager, built two clubs from nowhere”. 🇩🇪 #MUFC“Man United will be organised on the pitch. That's obviously not good news for other teams”. #LFC https://t.co/WMG4lHQW7rRalf Rangnick is gearing up to take on a tough challenge in one of the toughest and most lucrative jobs, as Manchester United manager. On that note, let's take a look at five managers who have rejected the opportunity to manage The Red Devils in the past.#5 Jurgen KloppJurgen Klopp has embodied Liverpool's spirit, and has made Anfield a formidable fortress during his tenure.Jurgen Klopp is one of the most passionate and outspoken managers in football. The German rose to prominence with Borussia Dortmund, winning successive Bundesliga titles in 2011 and 2012. Klopp was successful in knocking Bayern Munich off top spot in German football. He also guided the Black and Yellow to the UEFA Champions League final in 2013.Klopp's fiery approach and ability to rally his troops to grind out results seemed like a match made in heaven with Manchester United. Sir Alex Ferguson even approached the German to be his successor in 2013, but to no avail.Sky Sports Premier League@SkySportsPLLiverpool boss Jurgen Klopp reveals he rejected Manchester United job in 2013: skysports.tv/2SeuVP #LFC #MUFC2:48 AM · Jan 16, 2016179200Liverpool boss Jurgen Klopp reveals he rejected Manchester United job in 2013: skysports.tv/2SeuVP #LFC #MUFC https://t.co/Sw8lOLvaNHSpeaking to Sky Sports in 2016, Klopp revealed he had spoken to Sir Alex Ferguson, but he was unaware of a formal offer from Manchester United. The German explained that his loyalty to Dortmund, their players and the plans for the following season meant United's offer to him was ill-timed. Klopp said:"We spoke. We spoke not a lot but, for me, it was a lot. It was a big honour, the whole talk, to be honest. But I could not leave Dortmund. You are in April, and you are in the middle of the planning for next season. You have this player and this player who are coming, but then you are not there anymore? That doesn't work. Not in my life."He added:"I didn't hear about a real offer (from United) but, if there was, I could not have done it. I first had to finish the job with Dortmund, and then think about other things. "Klopp has since become Liverpool manager, and has helped the Reds win the Premier League and the UEFA Champions League. United and their fans can only wonder what might have been.#4 Carlo AncelottiCarlo Ancelotti is widely known for his successes in the UEFA Champions League as a manager.Carlo Ancelotti is another manager who was on the shortlist to replace Sir Alex Ferguson as Manchester United manager in 2013.The Italian established himself as a serial winner across Europe. He won league titles, cups and four Champions League trophies during his spells at AC Milan, Chelsea, Paris Saint-Germain and Real Madrid. The Italian is arguably the manager with the most widespread success in Europe's top competition.Squawka Football@SquawkaCarlo Ancelotti is the only manager in #UCL history to guide a club from each of Europe’s top five leagues to the knock-out stages:🏴󠁧󠁢󠁥󠁮󠁧󠁿 Chelsea🇫🇷 PSG🇩🇪 Bayern Munich 🇪🇸 Real Madrid🇮🇹 AC Milan, NapoliNow he’s done it with two Italian clubs. *mic drop*4:14 AM · Dec 11, 20191713540Carlo Ancelotti is the only manager in #UCL history to guide a club from each of Europe’s top five leagues to the knock-out stages:🏴󠁧󠁢󠁥󠁮󠁧󠁿 Chelsea🇫🇷 PSG🇩🇪 Bayern Munich 🇪🇸 Real Madrid🇮🇹 AC Milan, NapoliNow he’s done it with two Italian clubs. *mic drop* https://t.co/5YVteqX9QlAncelotti is known for setting his teams up in a rigorous 4-4-2 formation, allowing talented and highly skilled players to seamlessly co-exist. He was initially doubted by many for his defensive tactics and tactical ineptitude. But he proved his doubters wrong with a classic diamond in his midfield four. His reputation meant Ancelotti was a candidate for the Manchester United job.Speaking to The Independent in 2020, Ancelotti revealed why he turned down Sir Alex and Manchester United. He explained that there was already a project at hand at Real Madrid, referring to their quest for their tenth Champions League triumph, dubbed as La Decima. Ancelotti said:"You want to know from me? I can say that I still keep a fantastic relationship with Sir Alex, and we met when he decided to stop. But I was close to Real Madrid, and we had a job, and so I appreciate the fact that at the time he talked to me. And that's it, no other opportunity."Ancelotti did, in fact, go on to win 'La Decima' with Real Madrid that season. He is currently back in his second stint at Madrid after a short spell at Everton.