It cost the club as much to lure him from Internazionale, as it did to bring Cristiano Ronaldo, the world's most expensive player, to the club a year earlier – about £80m, including his salary, those for his entourage and a pay-off to his predecessor, the Chilean Manuel Pellegrini.
It was a desperate roll of the dice. The 2009-10 league race had gone down to the last weekend of fixtures. Real Madrid set a points' record, but were still bettered by Barcelona, who amassed 99 points to retain their title in a race that Pep Guardiola, Barca's manager, called "f*****g barbaric". To seek redress, Florentino Perez, Real Madrid's president, announced that his next major off-season trade would be Mourinho, his "galactico on the bench". At Inter, Mourinho's greatest achievement, the Champions League victory of 2010, was built on the back of a tactical shackling of Barcelona in the semi-finals.
As Real Madrid coach, his encounters with Barcelona have been controversial and chaotic, and have generally ended in ignominy and defeat.
This evening's match, the first meeting between the teams in the league this season and the first since the nadir of Mourinho's spiral into villainy in the Super Cup game at Camp Nou, is the first in which his team have not been playing some kind of catch-up to Guardiola's Barca.
Mourinho is finally looking as if he is the shrewd, savvy, winning manager who ruled the roost in England and Italy. During his first year in charge at Real Madrid, he left a trail of destruction in his wake. Around the Clasico fixture, he was incendiary.
The season came to a head during 18 fractious days in spring when Real Madrid met Barcelona four times. The first game was a 1-1 draw in the league at the Bernabeu, which preserved Barca's eight-point lead, effectively securing the title. Four days later, Real Madrid extracted revenge by winning the Copa del Rey 1-0 in extra time, courtesy of a scorching header from Ronaldo.
With the pressure mounting on Barcelona, Guardiola, their manager, finally cracked after a season of goading by Mourinho. He exploded on national television, cursing twice – sarcastically calling Mourinho "the f*****g man" – during a 45-minute tirade, the day before the sides met for the first leg of the Champions League semi-final.
The outburst had the desired galvanising effect. Barcelona beat Real Madrid 2-0, Leo Messi's brace being the only away goals scored in the Champions League at the Bernabeu during Mourinho's reign to date.
In the press conference afterwards, Mourinho cried havoc, lurching between indignation and disbelief in a fit of pathos. "Why?" he kept asking. He was disgusted with this world, he said. He longed to return to the bosom of his family. He had been foiled by the ref, a patsy, like three others he named from the refereeing trade who did the dirty work of larger, mysterious forces. His slanderous allegations, including a dig that Guardiola's previous Champions League crown was "tainted" and the suggestion that Barcelona's association with UNICEF afforded them special treatment from referees, brought about a five-match UEFA ban (subsequently cut to three on appeal).
Mourinho was unperturbed. In August, the Clasico rivals met in the Spanish Super Cup. Barcelona again prevailed, winning 5-4 on aggregate. In injury time in the second leg, a melee broke out by the dugouts. Both teams and benches piled in. Mourinho drifted into the fray and gouged the eye of Barcelona's assistant manager, Tito Vilanova. When pressed about it afterwards, Mourinho said he didn't know who "Pito" Vilanova was. Pito, in Spanish, is slang for penis.
Tomas Roncero, the Alan Hansen of Spanish TV punditry, said that Mourinho has turned Real Madrid into "a Mexican gang like Pancho Villa's Army".
He has been largely restrained, though, since the scandal of the Super Cup. With good reason: Real Madrid have been in imperious mood. They have sailed through the group stages of the Champions League and opened a six-point lead on Barcelona (reduced to three points with a game in hand), ahead of tonight's first Clasico in La Liga this season. It is the largest lead the club has had on Barca since 2003 and victory would be seen as a pivotal moment in the balance of power in Spanish football.
Both teams cruised into the knockout stages of the Champions League and their rivalry could again decide who takes the honours there, too.
In Spain, they say Mourinho's bocazas (big-mouthed). He is all of that and his direct jousts with Barcelona have, for the most part, ended in failure and even disgrace. But if anyone can loosen the Catalan grip on major prizes, it is surely Mourinho.
He has rebooted Kaka, once the world's most expensive player, who lost his way before Mourinho arrived at the Bernabeu, and his fellow Portuguese, Ronaldo, has also improved in the past two seasons.
Despite his rants about conspiracies and refereeing ineptitude, it is a lack of discipline that has often hurt Real against Barcelona, at a time when Mourinho was guilty of as much himself. In the seven matches against Barca since he arrived at the Bernabeu, his Madrid team have finished with 11 players on only two occasions.
If, this time, Madrid can reflect the regained composed confidence of the Special One, this Clasico could see this great Barcelona team fatally wounded in the pursuit of a fourth consecutive La Liga title by their great rivals, and the man they love to hate.