It was not inconceivable but it did seem unlikely that Kevin Pietersen would play 100 Test matches for England. That he does so on Thursday says much about his fabulous ability and something more about a ruthlessness in him that is not always apparent.

He is close to being regarded as a truly great cricketer, England's first since Ian Botham, because of a unique talent that has been relentlessly pursued. For all the paradoxes that make the man, Pietersen's batting brooks little argument. He has brought immense joy and single-handedly changed the course of many a Test match. Few in the history of the game can claim such influence.

Yes, he has moved in mysterious ways, often betraying both insecurity and vulnerability. He has taken unpopular decisions - "It's not easy being me," he once said - the consequences of which have been carried by others as much as by Pietersen himself. He admits to mistakes and to moments he might revise but even the contrition cannot disguise the fact that most of his actions are carefully enough conceived.

Flippantly, one might say that there have been three ages of KP - the skunk, the sulk, and the salvation - and add that brilliance has sat within them all. The edition we see today is close to the finished article. He has mellowed and, though self-absorption lingers (how can it not if excellence is to be achieved?), his generous references to the current England team are from the heart and have a relevance he may not previously have appreciated.

He is 33 years of age, a productive time for batsmen. The eyes are still sharp, the brain is calm. The impatience seems settled and the longing for acceptance resolved. Not so long ago an outsider, he is reintegrated. Champions are born with their gifts but otherwise are self-made. It's a process that takes courage, a feature of his make-up that is often ignored. And it is a risky business, with an attitude and reputation permanently on the line.

Initially he went out on his own, listening only to himself while travelling the rocky ground of adoption from one country to another. Marriage and a son have helped him see the other side. As has his present captain, Alastair Cook. Pietersen needed a "kitchen cabinet" more than he knew and it is serving him well. His work ethic has never been an issue, much blood and sweat has been shed and it shows in the record books.

A casualty of Pietersen's one unforgiveable misjudgement was the popular former captain Andrew Strauss. The defamatory texts Pietersen fired off to the South African team a year and a bit ago were more than just daft, they were provocative and threatening. A weary Strauss could take no more and Pietersen was left out of the England side for the final match of the series, which was lost. Days later Strauss retired from the game.

"Few cricketers have genius in them. A couple are noted here and others include Garry Sobers and Viv Richards. Pietersen may well be one of them"

The new captain, Cook, resolved to unravel the Pietersen problem, seeing the magic in the batsman as an essential advantage and the individualism in the man as something to point in the right direction. First Cook convinced the dressing room that they were not angels themselves and then he went to work on the problem. The theme of his approach was: what do you want Kev, greatness or great wealth? Doubtless he added that both were at his fingertips.

Pietersen saw straight, admitted fault, toed the line and turned the corner. He holds Cook in high esteem, an opinion that is well deserved. The strong characters in this England team require the touch of a surgeon. Cook has it, even if Shane Warne hammers on about other arguable flaws. But this is not Cook's story of 100 Tests - a mark that is a couple of matches away.

This is the story of a Pietermaritzburg boy who raged against the machine in the land of his birth. He blamed the quota system for his lack of exposure in the KwaZulu-Natal team and he had a point. After a dull season in the Birmingham Leagues, where the accents and pitches were equally indistinguishable, Clive Rice invited him to Nottinghamshire. The positive reply came by return post. Trent Bridge provided a fine theatre and the showman began to attract interest from important people as much for the substance in the performances as the style with which they were played.

He is of an Afrikaans father, an English mother and a disciplined upbringing that he remembers fondly. After a four-year period of qualification, the English mother provided the opening he craved and a new life began. England chose him for 50-over cricket first and his batting soared. The South African crowds hated the apparent haughtiness as he flayed their bowlers but by the third hundred, in the 2004 one-day series, they gave in and began to cheer the wonder of it all.

His first Test was against the Australians and began the Ashes of 2005. There is a nice symmetry in that his 100th does the same on the other side of the world eight years later. A hundred Tests in a little more than eight years tells you something important about the modern game. There is too much of it and players cannot possibly excel every time they take guard. Having said that, Pietersen's game of risk has an average of more than 48 per Test innings.

It was immediately obvious that the world was changing in that first game at Lord's when he hit Glenn McGrath over mid-off and into the Pavilion, before swatting Warne over midwicket into the Grandstand. England's batsmen had not been so brave or brash since their names were Botham or Gower. It is to Botham that he has sometimes turned for guidance, and having moved from Nottinghamshire to Hampshire, he found things in common with Warne too. At the after-show parties, he stood close by Andrew Flintoff.

The England captaincy changed things. He showed statesmanlike qualities in India after the Mumbai bombings and fuelled by the promotion and its trappings, went after the coach, Peter Moores. This became a crusade and cost him the job not long after he had received it. Moores was of county stock, a decent man of method and discipline to bring something structured from the young.

Pietersen was more for freewheeling and expression. He went behind backs and left the suspicion that he had diminished the entitlement granted by his adopted country. Nonsense. He wanted the right man in the job but those in power who could have helped him achieve it ran for cover. The truth is that soon after appointing Pietersen, the ECB regretted it and hung him out to dry.

Not until the tour of Australia three years ago did he emerge from the shadow. Then he played with an old abandon, completing a memorable double-hundred in Adelaide, alongside other worthy contributions. Never, though, can he have constructed a more meaningful and outrageously skilful innings than the one at the Wankhede Stadium in Mumbai late last year. England were a game down, two wickets down and 259 behind when he came to the crease on an extravagantly spinning pitch. When he left it, 233 balls later, England were 55 in front and he had made 186 runs of such flamboyance and magnificence that even the Indians found warmth in their appreciation. From that day - and from the captain's batting too, one should add - came England's series win, a triumph so against the odds that bets were almost off. Even there.

Few cricketers have genius in them. A couple are noted here and others include Garry Sobers and Viv Richards. Pietersen may well be one of them. He performs deeds that others dream of, turns matches, annihilates opponents and thrills audiences. He is the fastest batsman, in terms of days, to 4000, 5000 and 7000 runs. Now, in all international cricket he has scored more runs than any other England player. His pride - amazement perhaps - in this achievement is evident. It has come from hard graft and forensic attention to detail. The flair is not by chance, it is by design, but an entertainer's arsenal is filled with contradiction. For the highs there have been lows; alongside the gasps of admiration there have been sighs of despair. The most remarkable thing about the weight of runs is the range of the ambition.

Happy in love and happy in life, Pietersen can walk to the middle at the Gabba and know that he has done himself justice. The crowd will fill their seats and the Australian cricketers will be aware of a great danger. His family will have flown from South Africa and England to salute the man they know and love. His game is working well; that ambition is undiluted. If he does not reward their faith in this match - and it will be a surprise if not - he will do so soon. The purpose is renewed, another chapter is to come.