No. 5: Margrethe Vestager

Margrethe Vestager was also in the Global Tax 50 2016, 2015, and 2014

Amazon is the latest company to be slapped with a bill from Vestager for illegal state aid. The decision said the online retailer had received approximately €250 million of illegal tax benefits as a result of a tax ruling granted by Luxembourg. The ruling had lowered Amazon's tax bill without any valid justification, Vestager said, and allowed the company to avoid paying taxes on three quarters of its profits.

€250 million isn't a whole lot of money compared to the amounts in other cases Vestager has taken on – famously, Apple was fined €13 billion in August 2016 for allegedly receiving illegal tax benefits from Ireland. When the money still wasn't recovered by October this year, Vestager's patience wore thin and she took Ireland to court for moving too slowly.

"More than one year after the commission adopted this decision, Ireland has still not recovered the money," Vestager said. "We of course understand that recovery in certain cases may be more complex than in others, and we are always ready to assist. But member states need to make sufficient progress to restore competition. That is why we have today decided to refer Ireland to the EU Court for failing to implement our decision."

Ireland replied by saying it had never accepted the Commission's state aid decision, and said it was "extremely disappointing" that the commission had decided to take action.

The commissioner's investigations into Apple, Starbucks and McDonald's have given her a reputation of being on the warpath with Silicon Valley, and many politicians and CEOs across the Atlantic are weary of her singling out American companies. Responding to these allegations the commissioner simply stated that "it is irritating when American companies pay less in taxes than European ones".

Vestager recently confirmed that the fight will go on. On the question of future tax investigations, Vestager shook her head and said: "I don't think we're done. We haven't changed the full corporate culture yet."

The Dane has also been involved in a long-running state aid dispute over corporate tax exemptions for ports, which began in 2013, and in August she told France and Belgium to get rid of exemptions because they "distort the level playing field and fair competition". While the countries must abolish the exemptions by January 1 2018, they will not have to recover any of the aid, the commissioner said.

Vestager has made it her mission to address tax avoidance by multinationals through competition and state aid rules – something that makes her stand out from predecessors. With her term as competition commissioner running until 2019, multinationals will be holding their breath for at least two more years.