By Stephen Mulvey
EU reporter, BBC News
Neelie Kroes, aged 66, is the woman charged with keeping the playing field level for European business.
Ms Kroes has denied pursuing a vendetta against Microsoft
As competition commissioner, she has three key responsibilities: taking action against price-fixing cartels, disallowing mergers that would restrict competition, and ensuring governments do not unfairly subsidise industry.
She almost did not get the job.
In 2004, MEPs forced incoming Commission President Jose Manuel Barroso to drop his proposed justice commissioner, Rocco Buttiglione, and questioned loudly whether Ms Kroes was too close to the businesses she was set to police.
At the time, the former Dutch transport minister was on the board of 12 companies, including Volvo and the French defence group Thales. She had also worked as a lobbyist for Lockheed-Martin.
But Mr Barroso refused to withdraw the nomination and Ms Kroes survived a bruising parliamentary hearing, where her reputation was attacked by compatriot Paul van Buitenen, the one-time commission whistleblower turned MEP.
So she took up her job in the Barroso commission in 2004, having sold her shares and put her money in a blind trust, and having promised to take no part in cases involving the 30 or so companies she worked for during her business career.
She also vowed not to return to the private sector after leaving the commission.
But the idea that she would be too soft on business soon evaporated.
In 2007, the European Commission has imposed record fines on cartels, including the biggest-ever - of nearly 1bn euros (£0.69bn) - on four lift and escalator makers.
She has also been forced to deny pursuing a vendetta against Microsoft after fining the company for failing to comply with demands made by her predecessor, Mario Monti, and warning that the Vista operating system could fall foul of competition law.
Ms Kroes has been one of the loudest voices in the commission calling for European energy giants such as E.On and Gaz de France to be forced to sell off their distribution networks
After some tense months in 2006, Microsoft made changes to Vista that Ms Kroes said left her a "happy woman" - but the disagreements over the Monti ruling have only now come to a head.
Neelie Kroes (the first name rhymes with "daily" and the second with "mousse") spent 11 years in government in the Netherlands, seven of them as transport minister, representing the free-market liberal VVD party.
She spent the earlier part of her career in the family transport business, as a professor of transport at Erasmus University in Rotterdam, and as a member of the Dutch parliament.
After leaving government in 1989, following a short stint as an adviser to EU transport commissioner Karel van Miert, she became president of the Nijenrode business school.
In that capacity, she presented an honorary degree to Microsoft president Bill Gates in 1996.
Correspondents say Ms Kroes has sharper political instincts than her predecessor, Mr Monti, an academic economist and university president.
She is also more down-to-earth than her Dutch predecessor on the commission and fellow VVD party member, Frits Bolkestein.
Neither man would have been likely to invite members of the Polish Solidarity union for talks in Brussels after they protested against EU rules restricting subsidies to the Gdansk shipyard.
But she is not shy of upsetting big corporate interests, or even member states.
Ms Kroes has been one of the loudest voices in the commission calling for European energy giants such as E.On and Gaz de France to be forced to sell off their distribution networks.
That is another battle that is just coming to a head, with heavyweights France and Germany on the opposite side of the barricade.