Guus Hiddink and Louis van Gaal are two very different characters with a long rivalry that has seen them do battle in the Netherlands, Spain and England. Wesley Sneijder— who has played under both—described Van Gaal as the "tough school teacher" and Hiddink as "the friendly uncle," per Sky Sports.
Simon Kuper of ESPN FC wrote in December 2015:
...the last two relics of the legendary Dutch Seventies still working in top-class soccer have never got on. The boastful, humourless Van Gaal irritates Hiddink. Van Gaal, for his part, considered Hiddink a pragmatic, unadventurous coach.
"The way Guus Hiddink has his teams play, I don't like it all," he said once in the years before he created the dullest Manchester United in memory.
They first faced off as managers in 1998. Their acrimony was well under way by that point as they "refused to shake hands or acknowledge each other before their first meeting in September 1998, when Real Madrid hosted Barcelona," per Sky Sports.
"I will never go on holiday with Van Gaal," said Hiddink at the time, per Chris Wheeler of the Daily Mail. In December 2015, Wheeler wrote of the incident:
...there wasn't so much as a nod of recognition between the two Dutch coaches of Real Madrid and Barcelona. No handshake, no greeting, no acknowledgement that the other existed.
"Hiddink and Van Gaal fighting a silent war in Madrid," declared the headline in De Volkskrant newspaper, labelling the pair "Dumb and Dumber" for ignoring one another in a game of what the Dutch call stommetje while five Holland internationals on the pitch embraced warmly before kick-off.
Hiddink said on Friday, per the Express: "We have both had a long career but we haven’t met with a lot of frequency, in Spain a few times and in Holland a few times."
Sky Sports breaks down the occasions on which the two managers have met. Beginning with that Clasico in September 1998, the two men have faced off seven times, with Hiddink's sides winning four, two draws and Van Gaal's only victory being a 3-0 win when Barcelona and Madrid met at the Camp Nou in February 1999.
Hiddink beat Van Gaal's Barca with Real Betis in 2000 and won all three of the meetings between PSV Eindhoven and AZ Alkmaar when the two men were in charge. It was not until after Hiddink had left Eindhoven for the Russian national team that Van Gaal achieved one of his most remarkable feats by steering AZ to the Eredivisie title in 2008/09.
Van Gaal won La Liga with Barca in the season Hiddink was Madrid manager, finishing 11 points ahead of what had been his rival's side. It had been Hiddink's first season in charge, but he had been sacked in February.
His later win over Barca with Betis proved a Pyrrhic victory as he was sacked there, too, after just a few short months in charge.
Elko Born, writing for ESPN FC in December 2015, said:
If Van Gaal is the "Iron Tulip" of Dutch football, Hiddink is the "Velvet Rose." Far from having a set way of doing things, the caretaker manager of Chelsea likes to let go, rather than grab control.
Why stifle your squad with instructions when you can just let your best players do what they do best? For Hiddink, an arm around the shoulder and a nice compliment does more than all the video analysis and post-training lectures about the merits of possession in the world.
Wheeler suggested that that the fundamental in approach between the two men was exacerbated by Hiddink's friendship with Johan Cruyff, whom he describes as Van Gaal's "nemesis":
Cruyff became an arch critic of Van Gaal during his time in charge at Barca, and further riled him by complimenting Hiddink's Real for playing better football more in keeping with the Dutch model. Van Gaal, on the other hand, has been quietly critical of Holland's performances under Hiddink.
The national team situation has been a key battleground for the two men. During Hiddink's first tenure, Van Gaal was Ajax coach, a hugely influential and important position within Dutch football.
During Euro '96, Wheeler says Hiddink "saw that campaign undermined by a simmering feud between the eight players selected from Van Gaal's Ajax, ending with his decision to send home Edgar Davids for dissent."
In more recent times, Van Gaal may have indulged in some schadenfreude from Hiddink's failure to adequately replace him after the 2014 World Cup. Van Gaal left the Netherlands side on a massive high having guided them to third place in Brazil—a result that outstripped all expectations before the tournament.
Hiddink struggled terribly in his brief time in charge after that. He resigned within a year, saying, per the national team's website (h/t the Daily Mail): "I am sorry it went this way I thought it was an honour to again coach the Dutch national team and I wish my successor, the staff and the players every success on the way to the European Championships in France."
Of course, they did not make it to France. Hiddink failed to get anything like Van Gaal had done out of the squad and left too big a deficit for Danny Blind to make up.
Peter McVitie of Goal.com wrote of Hiddink's most recent time in charge of the national team:
Having pledged to improve on Van Gaal’s work, Hiddink completely tore it apart and left the national team in tatters. Reverting to a 4-3-3 formation, Hiddink made mistakes with every selection and never learned from them. He could not turn a game around and somehow even rendered Robben an ineffective bystander.
So each has had victories over the other, and history will remember them both as successful, if wildly different in their approach.
Ian Herbert of the Independent wrote in December 2015:
Neither has ever lacked self-confidence, though Hiddink’s more winning ways with the press are the part of his armoury which has failed to impress Van Gaal down the years. "I explain much more than Hiddink does," Van Gaal once said. "He never says a great deal. Hiddink is a master of not answering questions. I always answer questions."
Herbert wrote of Hiddink:
He is collegiate, democratic and can operate in a way which brings the best from his group. They like to say in the Netherlands that Hiddink was born a Protestant and lives as a Catholic, while with Van Gaal the opposite applies. The Cavalier and Roundhead at work.
Of course, the managerial battle never tells the full story of a football match, something that Hiddink was at pains to point out before the latest clash between the two as Manchester United face Chelsea on Sunday at Stamford Bridge. He said, per FourFourTwo:
We must not overvalue the role of the managers and the coaches - they prepare the games and the opponent and the way we like to play. That's it.
At the end the players have to execute what you are doing in training and in team meetings. We must not overvalue the battle between managers; it's a battle between the players.
The battle may be between the players, but in the case of Hiddink and Van Gaal, the rivalry certainly exists between the two managers.