Chelsea's most puzzling player provokes two obvious questions. The first is to satisfy pedants: what, once and for all, is his name?

Mikel John Obi, John Obi Mikel, Obi John Mikel, John Mikel Obi? "His first name is John, Michael is his confirmation name and the family name is Obi," says the player's father, Michael. Mikel – the name that is emblazoned across the back of his Chelsea and Nigeria jerseys – first appeared as a typo on a team-sheet when he represented Nigeria at under‑17 level. He liked the sound and appropriated it. "He considers that his football name," says his father.

The second, more interesting riddle is not yet adequately resolved: what does Mikel actually do? Some Chelsea fans deride him as a passenger on their team, others hail him as an unsung driving force, while many struggle to form any solid opinion of him at all, so inconspicuous has he tended to be since his arrival at Stamford Bridge four years ago. Now, it seems, is the time for Chelsea's invisible man to reveal his true self. There are signs that a very important player is beginning to emerge, one who even has the potential to control the game of the weekend at Stamford Bridge this afternoon, when Arsenal are the visitors.

There was never supposed to be any doubt about Mikel's function: he was to be a superstar. That was the notion that spurred Chelsea and Manchester United into a bitter battle for his services back in 2005.

United believed it was they who had successfully completed the then 18-year-old's transfer from the Norwegian club Lyn Oslo but there followed a bizarre series of events during which Mikel went missing from Norway without leave, prompting United's assistant manager, Carlos Queiroz, to accuse Chelsea of "kidnapping" the youngster. A few days later Mikel turned up in London and announced that he had only signed for United under duress and really wanted to join Chelsea. Much wrangling and threats of legal action ensued before Mikel, after three months without playing, returned to Oslo. Eventually, Chelsea acquired the player after paying the Norwegians £4m and United £12m. It is not certain that anyone would pay as much for Mikel now, yet at the time Chelsea obviously thought £16m was an acceptable fee for one of the planet's brightest prospects. Yes, he really was one of football's brightest prospects: at the 2005 Under-20 World Cup Mikel had inspired his country all the way to the final, where they lost 2-1 to Argentina. He was proclaimed the second-best player of the tournament – just behind Lionel Messi.

"He was a very exciting player, one of the most talented I ever saw in that category," the manager of that Nigeria team, Samson Siasia, tells the Observer. "He made a lot of runs, played a lot of through balls and was always involved in goals. It was like he had four eyes – he always knew where the ball was coming from and where he wanted to put it." He still had those qualities when he arrived at Chelsea, convincing Didier Drogba to assure Observer Sport Monthly in 2007 that Mikel would be "the next great African midfield player, and that means one of the very best in the world".

That prophecy, like Mikel's potential, has yet to be fulfilled. Most Nigerians blame the club rather than the player. José Mourinho deployed Mikel, now 23, not as a creator but as an enforcer. In his first full season he had more red cards than goals. He was told to calm down if he wanted to retain even a limited role in the team. Gradually the young recruit, whose effervescence had already, according to friends, been diluted by the discomfort he felt when he found himself the subject of a controversial tug-of-war between two of the biggest clubs in the world, became an almost nondescript player, a midfielder without any obviously outstanding qualities, except maybe the ability to execute endless short, sideways passes.

Mikel has not scored for his club since a 6-1 FA Cup victory over Macclesfield in January 2007. The 23-year-old's principal contribution to Chelsea attacks over the past few seasons has been to drop back to help the central defenders cover for Ashley Cole when the full-back embarks on one of his regular raids down the left.

"Chelsea destroyed the player Mikel once was," Siasia says, groaning. "They did a lot of damage to Nigerian football. Here was a young, enterprising midfielder who was going to be like Jay-Jay Okocha. He was about opening up defences, not protecting them."

Nigeria have never stopped using Mikel as an attacking midfielder but although he was credited with assists for nearly three-quarters of the goals the Super Eagles scored in qualifying for the last World Cup, which he missed through injury, he has not soared to the heights of greats such as Okocha.

"That's because he has been like a man with two minds," Siaisia says. "At Chelsea he's had to play defensively and then when he comes to Nigeria he's expected to be the offensive director. That's a very difficult transition for a young guy to keep making. If Chelsea start to use him offensively, that will really help him. At last he could explode."

The good news for Nigeria, and the bad news, perhaps, for the rest of the Premier League, is that Chelsea are now trying to coax more from Mikel. With Michael Ballack, Joe Cole and Deco all having left in the summer, Carlo Ancelotti has encouraged the Nigerian to resurrect his creative qualities, even if he generally remains the deepest-lying of the team's midfielders.

"John can basically become whatever he wants," Ray Wilkins, Chelsea's assistant manager, says. "He's got a lovely range of passing, is strong as an ox and reads the game exceptionally well. Myself and Carlo have just asked him to hit a few more progressive passes."

Mikel has obliged. Right from the opening game of the campaign he began to assert himself more, venturing into positions to which he hitherto had not dared to go. He set up Chelsea's first goal of the campaign, pouncing on the ball in the West Bromwich Albion penalty area after Scott Carson had spilled Drogba's free-kick and dinking it to Florent Malouda. The following week he created another goal by dissecting the Wigan defence with an astute pass to Nicolas Anelka.

Whereas in the past he seemed to abdicate as much responsibility as possible to more assertive team-mates, this season Mikel has emerged as the chief conduit of Chelsea's play. He averages more successful passes per game (73.1) than any other player in the Premier League – and the percentage of his distribution that has been directed forward (38%) has more than doubled since last season. In fact, his rate of sideways passes this term (55.8%) is significantly less than those of celebrated schemers such as Rafael van der Vaart (63.9%), Samir Nasri (65.4%) and Ryan Giggs (69.2%).

Mikel's renewed spirit of adventure has likely been stoked not only by his employers' new guidelines but also by the return to action of Michael Essien, who missed most of last season through injury. The Ghanaian is the one Chelsea midfielder with the energy and inclination to chase back and cover when Mikel surges forward. Mikel needs that help because he does not have the speed to retreat rapidly if moves break down when he is upfield, a fact that probably increased his inhibitions when Essien was absent.

As with Mikel, Chelsea have demanded more goals from Essien this season. "I told Michael and John that they are actually allowed to score goals," Wilkins jokes. Essien has responded by hitting three already this season. Mikel has made progress, too, his 20-yard shot against the crossbar at West Ham being the closest he has come to a club goal for more than three years. "He has a magnificent shot but if he ever scores it's going to cost me a lot of money!" says Wilkins, who has had a friendly wager.

Colin Udoh, of kickoffnigeria.com, one of the country's leading football writers, sums up Mikel's situation. "He's got so much quality locked up in there, he's almost like a coiled spring. But he's still not doing enough in my opinion to bring it out. I know that if he does he can be one of the best because he's got everything. If he can just develop that uncompromising will to win, then wow! But time is going, he's not a young player any more. He's got to get those things together."