The eternal understudy, Sergio Aguero

To call one of the best forwards in world football the eternal bridesmaid might be overdoing things a bit but at times it seems people forget about Sergio Agüero a little too easily.

At the club level he's scored a title-winning last minute goal, one that ensures he'll remain a part of Manchester City's history forever, but in the season just gone he -- along with, it must be said, all of his teammates -- have been as thoroughly overshadowed as opposing midfields by the performances of Yaya Touré.

And though many top players get the chance to step out of the shadows and into the limelight when they join up with their national teams, Agüero isn't one of them. How could he be with Lionel Messi in the same attack?

Agüero's talent is such that this frequent lauding of teammates feels somehow unjust, but the application of that talent stems from the fact that he himself doesn't particularly care about being the main man. His part in the team is all he cares about. This World Cup will be Agüero's second and his first with a proper manager; like everyone in the Argentina squad, he's determined to make it count.

An expert at ghosting into the box on the left when opposing defenders are concentrating on Messi on the right, Agüero's link play with the Barcelona genius will be vital for his country this summer. Argentina attack at pace and with quick passing exchanges; playing off Gonzalo Higuaín as a reference point in the middle, Aguer and Messi get on as well on the pitch as they seem to off it. Not for nothing are Barcelona said to be eager to sign the City forward.

With his creative qualities and speed of thought well known, perhaps the most underrated aspect of Agüero's game is his finishing. It seems a bizarre thing to say of a striker, but I rarely see much comment on it; the cleanness with which he strikes the ball is impressive, while his range of finishing too is comparable with any player in the world.

They're gifts honed from a very early age; he may have only turned 26 this past Monday but already Agüero has been playing professional football for eleven years. At the age of fifteen years, one month and three days old on his Independiente debut, he remains the youngest player ever to play in Argentina's top flight. He took that record from Diego Maradona, who would later become his father-in-law, albeit for a brief time.

Right from his debut it was clear he was something special. Sports daily Olé reported the next day that although his first meaningful action was to commit a foul, he soon settled into the game.

"Seven minutes after coming on, el Kun [as he's nicknamed at the club] brought the ball under control beautifully and set off on the attack. Later there was a one-two with [Federico] Insúa. The best moment was a quick burst through the defence with the ball, followed by a centre which [Maxi] Ayala didn't quite connect with."

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Agüero's a lifelong fan of Independiente and it was his 20million-euro sale to Atlético Madrid in 2006 that allowed the club to begin construction of their new stadium. Though inflation and slow building work mean it's still not finished today -- work was halted for a long time before his move from Manchester City brought a FIFA solidarity fee Independiente's way and meant it could restart -- but Agüero has, according to his father, offered the club money for signings on at least one occasion. The offer was turned down but it demonstrates that his passion for the game remains; it's more than just a livelihood for him.

Aguero's hard work and enjoyment of the game are both vital, and have brought results; 21 goals in 50 appearances for Argentina puts him joint ninth in Argentina's all-time top scorers list -- level with his team-mate Higuaín, who has 21 in 34 -- and his assists are also important. On Saturday afternoon he added another with a cushioned header which left Messi with a simple finish after both had come off the bench in the second half of a 2-0 win over Slovenia in La Plata.

That substitute appearance came after a knock had kept him out of the previous friendly, a 3-0 win over Trinidad and Tobago in Buenos Aires a few days before. Higuaín didn't play either match, but Agüero's return to fitness will be a huge boost to Argentina as they prepare to head for their training base in Belo Horizonte.

The real key is that while the world fixates on Messi and Ángel Di María's recent performances for Real Madrid have made him the man of the moment, Agüero is confident as part of the group and aware of his own importance to Argentina's chances of success. His relationship with Di María is important, too; the pair link up well down the left of the Argentine attack in their preferred 4-3-3, not to mention Aguero's ability to provide a shooting threat when he cuts inside.

Is he as important to the side as Messi? No, he's not. After all, Messi is'nt really questioned as the best player in the world even after a season during which, by his own standards, he's had a bit of a slump. Agüero's willingness to work for the side and to sacrifice himself for the team -- if Argentina switch to a 3-5-2, it's normally Agüero who drops out of the starting lineup to accommodate the change -- is arguably as important to maintaining a harmonious group as Messi's dribbles and passing are to the team on the pitch, though.

So don't feel too sorry for Agüero even if he can seem like perennially overlooked in some respects. He, along with the rest of the squad, knows he has a chance to be part of something historic. If that means playing second fiddle to a man who might well go down one day as the greatest attacker of all time, so be it.