It's hard to realise how special someone is when you see him on television all the time. Ronaldinho appears in Nike commercials, in kiss-and-tell stories in British tabloids, and in Spanish football matches. He has buck-teeth and always smiles. Often the Brazilian seems just another contemporary celebrity, like Paris Hilton or Prince Harry.
You have to remind yourself that he is also a genius, a man like Van Gogh or Nijinsky who does things in a new way that works and is of great beauty. This is the only remarkable fact about him. Yet people seldom look for genius in football, instead treating the sport as a branch of the celebrity industry. The recent Champions League match between Barcelona and Chelsea, the world's two best teams, was reported largely for the quarrel between their coaches.
When the teams meet again on Tuesday, with Chelsea seeking to overturn a 2-1 deficit at Stamford Bridge, better to concentrate on Ronaldinho. What makes him a genius?
No footballer has ever had a greater repertoire of feints. For his favourite, the "elastico", he touches the ball with the outside of his right boot as if to go that way. Then, t he instant the defender shifts his weight, he takes the ball the other way with the inside of his boot. This happens so quickly that you often only see it in the slow-motion replay.
But Daniel van Buyten, a former opponent, warns: "He never does the same feint twice in a row." Ronaldinho's arsenal includes bouncing the ball off his back over his own head; lobbing the ball over a defender's head (the "sombrero"); or stepping over the ball and running around the defender. Once, besieged by two defenders, he lobbed the ball over his head, then turned and lobbed it the other way, then did it again.
One feint, when he was still with Gremio Porto Alegre in Brazil, I watched several times before working out what had happened: Ronaldinho played the ball with his right foot behind his left leg, then, with legs virtually crossed, flicked it past the defender with that same right foot. This had probably never been done before. "There's no better way to confuse an opponent than to invent something," he says.
He doesn't only dribble. Once, about to receive a high pass, he suddenly turned and bounced the ball off his back to a team-mate's feet. He also plays the "no-look pass", which involves looking one way and passing the other. This can be comic, particularly if he is smiling. There is something of Harpo Marx about him.
The only common indicator to emerge from one study of genius was the propensity to practise endlessly. Ronaldinho did this. His father was Gremio's groundsman, his elder brother played professionally, and they trained him. As a kid, Ronaldinho dribbled so much that other children would get bored of playing with him.
"Luckily my dog Bombom was always ready to take over," he told the French newspaper L'Equipe. "I played against him for hours. I tried all possible feints to avoid him puncturing the ball."
Even today, Ronaldinho's mansion in Barcelona is stuffed with footballs, volleyballs and basketballs. When it rains he dribbles a tennis ball through the lounge. Few professional footballers live like this. Paco Seirulo, Barcelona's physical trainer, says: "I've never before talked to a guy with a ball stuck to his left ear."
All this play is purposeful. Ronaldinho spends hours rehearsing specific moves. Sometimes he draws inspiration from a photograph of a colleague's move. He copied the elastico from another Brazilian great, Rivelino.
But possessing the technique isn't enough. There are street footballers who can do Ronaldinho's feints. What sets him apart is firstly that he uses tricks functionally - often the elastico will be followed by a defence-splitting pass - and that he dares perform them in big games. This is rare. Samuel Eto'o, Barcelona's striker, says he learnt from Ronaldinho that "the most important thing is daring". Henkten Cate, Barca's assistant coach, cites as an example Ronaldinho's lob over the defence for Xavi's goal against Real Madrid last April: not only did he see the pass and have the technique to play it, but also he dared hit it.
The cliché is that his joy in playing is typically Brazilian: that Brazilian football is a thing set to music. This may be true. Ronaldinho says: "I play football with melodies in my head. I listen to dance music all day and take those sounds with me on to the field. That makes me happy, and the happier I am the easier I play."