The son-in-law of God appeared in Manchester on Wednesday. It was not the city Giannina Maradona's husband expected to turn up in when he announced that he was leaving Atlético Madrid. Nor was it the one El Diego foresaw. Maradona, who once advised Sergio Agüero to "run all the way to Inter Milan", leaving the Vicente Calderón in his wake, had been as adamant as he was categorical: in 2011-12, he said, Sergio Agüero would still be in Madrid – just up at the other end of the city, playing for rivals Real.

Maradona is prone to outbursts, prone to getting it wrong too. But he was not alone. Truth be told, the man they call Kun did not plan it this way. He had spoken to Juventus but hoped to force a move to Real Madrid, who had informed him of their interest. The delay in completing a move to Manchester City that had been in place for over a fortnight was caused by his desire to wait for his original suitor.

Atlético, though, did not budge. Real did, reluctantly giving their word that there would not be a hostile, and thus hugely expensive, bid. In the end, Agüero had little choice.

Yet if that sounds as if City fans should have misgivings, they should not. The greater reservations were not in Manchester, but in Madrid. Real fans are disappointed that the 23-year-old Argentinian will not be joining them. That alone hints at the fact that City have signed a genuinely special footballer, the man of whom the Lokomotiv Moscow coach declared: "Watching Agüero play is like visiting the Prado museum."

Nor should City necessarily fear a Tevez-style episode. The Maradona family makes for quite an entourage but Agüero is brighter and sharper than the countryman he describes as one of his heroes – something that comes as a timely reminder that he is still young. He is quiet in interviews but the hint of quick-witted mischief is confirmed when the tape is turned off; he will travel with his wife and two-year-old, Benjamín Agüero Maradona; and his forced departure from a declining Atlético appears more legitimate, in purely footballing terms, than Tevez's cries for freedom.

Bluntly, Agüero had become too big for Atlético. Deep down, Atlético fans knew that. There is cold comfort in him not staying in the city to rub it in daily. "He reminds me of Romário," Anatoliy Byshovets had said that night in Moscow, "except that he pressures all over the pitch and plays a greater role in the team's play." That night, Agüero had carried Atlético to victory. The kid who remembers playing five games a day as a 12-year-old, crisscrossing Buenos Aires dreaming up new gambetas (dribbles), and who at 15 years, one month and three days became the youngest footballer to play in the Argentinian first division, was only 19.

At that point, he had been in Spain 18 months and after a difficult first year – he ate too much meat, drank too much Coke and stayed up too late, Atlético insiders confirm – he was turning in superb displays with striking regularity. In March, Agüero beat Barcelona 4-2. And, yes, that does say 'Agüero' - the Argentinian providinged two goals, an assist and a penalty out of nothing. The Atlético-supporting columnist Iñako Díaz-Guerra raved: "In 30 years, I've seen some great players, from Hugo Sánchez, to Torres, Futre, Caminero and Kiko, but none ooze excellence like Kun," while his newspaper gave Agüero four stars – out of three.

That season, 2007-08, Agüero was Spain's outstanding player, taking Atlético to the Champions League for the first time in 11 years. When he played in the Champions League, Didier Drogba noted: "The only word I can use to describe Agüero is spectacular. I don't want to disrespect Atlético but great players end up at great clubs." The "And Atlético are not a great club" went without saying.

When Agüero signed off last season with an astonishing hat-trick it seemed to corroborate Drogba's view. Now that has been confirmed – not because Chelsea signed him, even if Carlo Ancelotti openly said, "every big club has looked at him", but because City have.

In a sense the surprise is that it has taken this long. Agüero may not have matched that second season but he has been remarkably consistent, even as the risk of stagnation hung over him. In the last four years, Agüero has scored 68 league goals. That's five more than Carlos Tevez. But it's not just about the goals; it's more about the inventiveness. "I play with shadows," Agüero says. He is not talking about his team-mates but at times he might have thought he was. "You two [Reyes and Agüero] are really destroying teams," José Antonio Reyes was told after one game last season. "Well, er, two?" replied Reyes. "Kun."

As Javier Mascherano notes: "Kun is dangerous because it's impossible to know which way he is going to go. His dribbling is a 10 out of 10 and his imagination is too: he never does the same thing twice – he is always inventing something new."

"His cutbacks, dribbling and chips are works of art," one Spanish newspaper has said. "Agüero is a virtuoso who's worth the entrance fee. He destroys his opponents with pace and strength, spilling creativity, ingenuity and pure talent all over the pitch."

For €45m City have bought a striker with a slight upper body but powerful legs and backside – he can leap 60 centimetres from standing. He never shirks physical challenges, once telling Fabio Cannavaro: "That round thing is the ball." Capable of exploiting the tiniest of spaces in penalty areas and the biggest of spaces outside of them, he is skilful, quick and clever; target man, goalscorer and playmaker all rolled into one. Indeed, for a No10, Agüero played much of his Atlético career further forward than the striker Diego Forlán, receiving aimless punts and turning them into something else,something good.