Some argue that it's his man-management skills. Others say that his tactical nous is unrivaled in the professional game. Judging by his success in his 11-year tenure as a manager, it would be hard to disagree with either of those points.
Yet, the humble Portuguese mastermind would tell you that without his backroom staff, he would not be so special.
No, we're not joking.
Once again, you can't help but agree with him. Steve Clarke, Andre Villas-Boas and Brendan Rodgers—who all worked under Mourinho during his first stint in charge—are now the managers of West Brom, Tottenham and Liverpool, respectively.
Given this, we've decided to take a look at some of Mourinho's trusted confidantes and the range of expertise they bring to the club.
Rui Faria (Assistant First Team Coach - Fitness & Conditioning)
The Portuguese fitness coach is regarded as a key figure in Mourinho's backroom team, and is widely known as his right-hand man, even though there are several members of the coaching staff who share the same title.
Although he specialises mainly in fitness and conditioning, Faria has been an important part of Mourinho's success. The two met in Barcelona while Mourinho studied for a degree in sports science and Faria was first introduced to his team at Uniao de Leiria, which was Mourinho's first managerial job. Faria has remained loyal ever since.
When Mourinho returned to Stamford Bridge earlier in June, he described Faria as the man "who understands best my information and the way I work." Often seen sitting next to the 50-year-old on the bench, Faria's lighthearted character enables him to form a strong relationship with the players, and his fitness methods are often imperative to Mourinho's title-winning squads.
Silvino Louro (Assistant First Team Coach - Goalkeeping)
A former goalkeeper for Portugal's national team, Silvino Louro can lay claim to one of Chelsea's most prized records and has helped develop two of the world's best goalkeepers.
Of course, in his first season in England, Louro used his wisdom to guide a young Petr Cech—who had just arrived from French club Rennes—towards greatness. In doing so, his knowledge and work with the Czech Republic keeper paid off, as Chelsea conceded just 15 goals in the 2004-05 season on their way to the title.
He also had a lasting effect at Inter Milan with Mourinho, working closely with Julio Cesar as the Brazilian entered a period of breathtaking form in 2010. Louro can also take credit for Cesar's improvement, as the Nerrazzuri won the Champions League.
Working alongside long-serving coach Christophe Lochillon, Louro played a key role in developing Thibaut Courtois and Matej Delac—who are widely considered the future goalkeepers at Stamford Bridge—into world-class players in the coming years.
Jose Morais (Assistant First Team Coach - Opposition Analyst)
The much-travelled Portuguese coach, who, like Louro, is a former professional player, is currently working in England for the first time in his career after several spells with Mourinho at Porto, Inter and, most recently, Real Madrid.
Morais' managerial stints in his homeland, as well as in Sweden with Assyriska, Africa with Esperance Tunis and Yemen with the national team, have seen him travel the world, literally. But, ideally, he sees himself as a part of Mourinho's backroom staff.
The 47-year-old will take on an analyst role similar to the one Andre Villas-Boas held at Chelsea and Inter before leaving, working with Chief Opposition Scout Mick McGivern. It's a role with much importance for Mourinho, as he likes to set up his tactics with a knowledge of what the other team are planning, and Morais' intelligence will provide him with that information.