There is an amusing moment in the new film about Cristiano Ronaldo when he is walking his son from the school gates and they are approached by another parent, a giant basketball player.

Young Cristiano is amazed by the size of the stranger, and Ronaldo briefly looks flustered by his son's awe at this new alpha male. "Big guy," Ronaldo acknowledges, "but Daddy's stronger."

And, boy, is he keen to prove it. Cut to Ronaldo doing press-ups with his son lying on his back, or having his boy help with sit-ups. We even see him comparing biceps with the five-year-old. You have never seen a father more desperate to be admired by his offspring, but that is the theme of the film and of Ronaldo's life, this craving for adulation.

"I was made to be the best," he says and, by the end of 90-odd minutes, that message has bludgeoned you over the head.

Ronaldo is so desperate to be idolised that he drops any pretence that football is a team game. The loose thread of the film is his obsessive quest not for the World Cup or Champions League but what he regards as the game's greatest honour, the Ballon d'Or.

Team-mates are simply extras in Ronaldo. There is not so much as an acknowledgement of Wayne Rooney or Gareth Bale, or any of them.

As for opponents, there is only one: Lionel Messi. Ronaldo is obsessed with bettering him. "I'm not coming here any more," he strops when Messi wins his fourth Ballon d'Or in a row in 2012.

Of course, we already suspected that Ronaldo had a planet-sized ego, but it all amounts to a far more intriguing and revealing film than I had expected, and not just because the camera tracks Ronaldo into the shower and to his underpants drawer (yup, literally).

Yes, there is glossiness, PR spin, buffing up and lots of lingering shots of his six-pack, but there is also the exposure of a complex personality that has driven Ronaldo to the pinnacle of the global game.

Football fans will enjoy it but psychologists may glean the most. They will be fascinated by the shots of Ronaldo rattling around a glass mansion in Madrid with no other company than Cristiano Ronaldo Jr, his son and mini-me. Or, as Ronaldo calls the young boy, "my successor". No pressure there, then.

If the relationship seems a little odd, and Ronaldo an unlikely single parent, it all begins to make sense when we hear about the death of his own father, a war veteran, from alcoholism. Dinis was largely absent through Ronaldo's life.

"He wasn't the father that I dreamt of having," he says. The words sound harsh but, underneath, there remains a deep yearning for approval. Dinis' portrait hangs on the wall above Ronaldo's breakfast table.

In this light, we understand Ronaldo's eagerness to have this son, to raise him, to be the doting father that he never had, summoning his boy for frequent kisses, trying to create a paternal ideal.

"He doesn't need a mother, just me - having a father is enough," Ronaldo says. He refuses to talk about the boy's mum; an American waitress who received £10 million (S$21.5 million) in one report, a surrogate in another. Whatever the truth, Ronaldo is not saying. "I have never told anyone and never will," he says.

There is no glimpse of a girlfriend, and few friends. "People I really trust? Not many. Most of the time I'm alone. I consider myself an isolated person," he says.

So we cut back to the curious shot of Ronaldo and his boy in their lavish home, his son playing spot-the-missing-sports-car. "The Porsche? No. The Ferrari? No. Ah, the Lamborghini," he says. Ronaldo looks on proudly.

And good luck to him. Ronaldo has worked incredibly hard to earn these riches since he bid a tearful farewell from the family home in Madeira, aged 12, a homesick child seeking his footballing fortune in Lisbon. Through devotion to his craft, he has lifted himself to become one of the greatest footballers in history.

His rise has enabled him to provide for his widowed mother, Dolores, who expresses her joy that she did not go ahead with plans to have an abortion. Ronaldo has helped his brother, Hugo, overcome addictions by putting him in charge of a CR7 museum back in Madeira.

There is much to admire but, just when you might learn to love Ronaldo, he sits amid the mess of Portugal's 2014 World Cup campaign and says: "I'm not gonna lie, if we had two or three more Cristiano Ronaldos in the team, I would be more comfortable. But we don't."

Just when you might be charmed, we cut to him sitting around a dining table, still obsessing about his status, demanding to know of friends: "Tell me the best player in the world?"

Jorge Mendes' role is always to be on hand to say, "You are, Cristiano!" Armed with Rolex, black suit and nauseating patter, we see the "super-agent" wandering between infinity pools, holding half a dozen phones, making billions by breakfast, constantly telling Ronaldo how amazing he is.

Driven by that need to be the very best, Ronaldo has never lost his focus despite this claustrophobic level of fame. "He knows I exist!" one woman screams, after scaling a fence and evading security guards to hug him. When Ronaldo becomes a godfather, the priest finishes the service by asking: "And now a quick selfie?"

Ronaldo is constantly in demand, a global megastar, but the lingering memory of the film - shot over 14 months by the same producers of the acclaimed Amy and Senna - remains the sight of him at home with just the boy. In one scene, they are lying on the sofa when Cristiano Jr says that he wants to become a goalkeeper. Ronaldo looks appalled. "A goalie? Are you joking, or what?"

Watching this, you wonder if Ronaldo even knows the name of Real Madrid's goalkeeper.

THE TIMES, LONDON