Louis van Gaal will resume a friendly rivalry with Jurgen Klopp when United face Liverpool at Anfield on Sunday adding a fascinating sub-plot to what is already the most historic and competitive rivalry between the English game's two most successful sides.
Van Gaal and Klopp are undoubtedly two of the most high-profile, charismatic, successful and quotable bosses in the league and they will do battle against each other for the fifth time this weekend.
Dortmund 1-5 Bayern (12.9.2009)
The two first met at the Westfalenstadion five games into Van Gaal's reign at Bayern Munich, when he endured a sluggish start but kick-started here, with the 5-1 win Bayern's biggest ever away to Dortmund.
Long-time United target Mat Hummels put Klopp's side ahead but, after Mario Gomez equalised, our very own Bastian Schweinsteiger put Van Gaal's side in front.
Franck Ribery made it 3-1 before young substitute Thomas Muller stepped off the bench to net a brace and clinch a one-sided victory (Muller became a regular starter for the Bayern first team from then on). Van Gaal 1-0 Klopp
Bayern 3-1 Dortmund (13.2.10)
Although Klopp's Dortmund took the lead in the return fixture at the Allianz through Mohammed Zidan, this would prove to be Klopp's 10th successive loss to Bayern as goals from Marc van Bommel, Arjen Robben and Mario Gomez ensured Van Gaal bagged another win over his German adversary.
The result left Bayern with a five-point lead at the top of the Bundesliga and Klopp bemoaned the referee's decision-making after the game.
"These mistakes from the officials do not make it more fun" he said.
Van Gaal 2-0 Klopp
Dortmund 2-0 Bayern (3.10.2010)
Van Gaal won the title at the end of his first season but, by the time this fixture rolled around his champions had recorded only eight point from their opening six games.
By contrast, Klopp's side were flying and extended their winning run to six matches with this comfortable victory thanks to goals from Nuri Sahin and Lucas Barrios.
It was Klopp's first victory over his Dutch counterpart and left his team ten points ahead of Bayern after seven outings.
"The season is very long so it is difficult but we must have faith" said Van Gaal.
Van Gaal 2-1 Klopp
Bayern 1-3 Dortmund (26.2.2011)
"It doesn't get any better" admitted Klopp after his youthful side had won at Bayern for the first time in two decades, thanks to goals from Barrios, Sahin and Hummels.
"We didn't win in Munich for 20 years: Sebastien Kehl was 11 and rest of the boys were still-being breast fed" said Klopp, whilst Van Gaal admitted the title was "already gone" with his side 16 points behind Dortmund with 10 games to go.
Van Gaal left Bayern two months later as Klopp went on to lift his first Bundesliga title in May.
Van Gaal 2-2 Klopp
Klopp on Van Gaal:
"Louis van Gaal is one of the most successful managers in the world.
"He has won a lot of titles and not only in Germany, he has a special idea about football and you have to respect him as an opponent.
"A game against Manchester United is a bit like Dortmund v Schalke, you can play the whole season how you want but you have to be prepared, at your best for these games.
"We both need the points to stay close to the top end of the table but it is Man United- I love derbies and I am going to love this game."