Many people consider Roger Federer to be the greatest tennis player of all time. But you would not necessarily count the agent of one of his fiercest rivals among them.
"Roger is a very nice guy. I think he's the best tennis player in history. The way he plays tennis is unbelievable. I love Roger," says Carlos Costa, who acts for Rafael Nadal.
Being a former professional player himself, it is perhaps not surprising that Costa is able to take an objective view on the talent of tennis stars.
Born and bred in Barcelona, Costa turned professional when he was 19. His highest career ranking was world number 10 in 1992.
Beating former world number one Pete Sampras may appear on the surface to be his best accomplishment, but it was by no means his most memorable match.
"It's not that I beat Sampras in a grand slam in the semi-finals," he says. "I beat him in a good tournament, but in the second or third round, which you can understand with the top players normally it's better to beat them in the semi-finals or finals of a grand slam. But it was a good match."
He is most proud of winning the Barcelona Open in 1992, a year when he played well for six months, claiming several titles. But it was tough to keep up the momentum.
"For me it was a great year," he says. "It was a surprise. And then after that you have to keep working hard to keep the level and keep improving. Maybe in that time I was a little bit surprised about my level and I wasn't so concentrated to improve things to keep at the same level."
For the last two years of his 11-year professional career, Costa began to manage himself, breaking away from his agent.
"I started to deal with my contracts and everything because it's something else I really liked," he says. "It was something I wanted to test and to see if I would be qualified for."
And as it turned out, he did have a talent for management, joining IMG, his former agency, as an employee in late 2001.
His boss passed him a number of clients when he joined the company, but he soon started to sign stars of his own, including David Ferrer, who was his first.
He signed Nadal in 2001 or 2002 - he cannot remember the exact year - when Nadal was about 14. The young Spaniard soon began his rise to the top, reaching the top 50 for the first time in 2003. Two years later he claimed a teenage record of 11 titles. He knocked Federer off the top spot in 2008, ending almost five straight years of the Swiss player's domination of the game.
"David Ferrer is still with IMG, but he is not with me any more, because if you are managing Rafa Nadal, you don't have any time to manage another top player," Costa says.
So what is the man he has represented for more than a decade like?
"He's like family for me and I'm like family for him," Costa says.
"He's so loyal. He has been working with the same team for 11 years already. Sometimes when [tennis players improve and] start winning … they don't like to listen to the people around because they think they are right. Rafa always has his people around and he listens to the people. It's very easy to work with him."
And he works "24/7" with Nadal managing his calendar and list of lucrative sponsors. But he refuses to reveal how much his contracts with them are worth.
"How much? How much he gets for the sponsors?" says Costa with a hint of irritation. "No, I never will tell you this. It's confidential."
Yet estimates of Nadal's earnings from endorsements are not hard to find.
He was the 12th-highest paid sports star in a Forbes list last year, earning US$31.5 million (Dh115.7m), $10.5m of which was prize money, in the 12 months to last May.
"We try to get the key strong points from Rafa, so a leader, a winner, he's a fighter, and then we try to find a company which has these points, in Spain or worldwide," Costa says.
Nadal's sponsors include Banesto, "one of the best banks in Spain", Mapfre, an insurance company which is the "best company in Spain", and Kia Cars - which "has been involved in tennis for many, many years".
So will this be the year that Nadal returns to the number one spot?
"I don't know. It's so difficult to gauge, but he's doing the right things," Costa says. "We will see. [In 2011, Novak] Djokovic played unbelievably. He won everything. Sometimes even if you do your best there is another guy who is doing better. There is nothing you can do. But he is doing the right things to stay on top."