“He is loyal to everyone,” Gil added, “and he does not play tricks on you.”

In fact, Mendes has a reputation — unlike many of his peers — for not chasing the quickest deal, but for encouraging his players to wait for the right moment to make a move. His first question to every prospective client is, “Where do you want to play?” In at least some cases, he presents his players with blueprints for their careers: Follow this path, he tells them, and you will get where you want to go.

It is an approach that has made his players — Ronaldo, Ángel Di María, Radamel Falcao and the rest — famous, and earned him not only a litany of plaudits but also considerable wealth, enough to make him the second-highest-earning sports agent in the world, after baseball’s Scott Boras.

But his success has been built not only on his sage advice. The Mendes network is central to it.

The beating heart is, of course, in his native Portugal. According to a 2011 brochure produced by Quality Sports Investment, a fund designed to buy the economic rights to players whom both Kenyon and Mendes advised, Mendes claimed he oversaw 68 percent of all transfer activity from the country’s three giant clubs — Benfica and Sporting in Lisbon, as well as F.C. Porto — between 2001 and 2010.

That is just the start, however. There is also a long list of smaller clubs where, according to Russo, Mendes places players from South America when they first arrive in Europe. These are the moves that provide his young clients with opportunities to play and that have, at times, helped him circumvent FIFA rules on outside investors’ — so-called third parties — owning the economic rights of players.

There are so many of these clubs that, when Portugal’s tax and customs authorities announced an investigation into Mendes’s transfer activity over the last three years, their list ran to 13 teams.

“Working with Mendes gives clubs like ours access to better players than we might otherwise be able to have,” said António Silva Campos, the president of Rio Ave, a first-division club that Russo calls F.C. Mendes, but one that is not part of that tax investigation. “There is no club in Portugal who does not want to work with him.”