No. 7: Sri Mulyani Indrawati

Sri Mulyani Indrawati was also in the Global Tax 50 2016

It is a post she previously held from 2005 to 2010. Furthermore, between her stints leading the economy of the world's fourth-most populous country, she worked as the managing director and chief operating officer of the World Bank Group. This is the World Bank's second-most senior position, making her the most senior woman in the organisation's history.

She has also previously worked as an executive director at the International Monetary Fund (IMF), and as the head of the Indonesian National Development Planning Agency. She holds an economics degree from the University of Indonesia and an economics doctorate from the University of Illinois.

But her place in the Global Tax 50 comes not because of her qualifications and career but because of the huge tax amnesty undertaken by Indonesia this year and last, and the tax reform following it. In a CNBC interview, she said she the tax reform brought "investment certainty and the fiscal certainty" Indonesia needed.

The government launched the amnesty in July 2016, hoping to repatriate around a quarter of the estimated IDR 4,000 trillion ($300 billion) of Indonesian money held offshore.

It offered staggered rates of 4% penalties for funds declared between July 1 and September 31 2016; 6% for funds declared between October 1 and December 31 the same year; and 10% for those declared between January 1 and March 31 2017.

Taxpayers could access lower rates still if they actually brought the money back into Indonesia according to "specific investment instruments… prepared by the Indonesian government and the financial authorities", including government bonds, state-owned enterprises' bonds, corporate bonds, deposits in state-owned banks, collective investment contracts and real estate investment trusts. In other words, the amnesty offered preferable rates to those willing to boost Indonesia's growth.

The amnesty, of course, came in for criticism as being a 'reward' for those who had avoided tax in the past. Indonesia is a deeply unequal country, with the richest 1% of its citizens controlling nearly half of the wealth. This criticism is weighed against the benefit of having people enter the tax system.

While the level of repatriated income fell short of its target, the tax amnesty overall was significant. Around $350 billion – equivalent to approximately 40% of Indonesia's GDP – was declared by around 750,000 taxpayers.

The taxpayer response to this initiative has helped to shape the next steps in Mulyani's plans for tax reform.

Mulyani, who was once considered interesting enough to have her phone hacked by Australia's spy agencies, wants to lift taxation to 13% of GDP – it is currently less than 11% – in the long term. She will do this through a number of reforms spanning greater cooperation and data sharing with other countries, improvements to the tax authority and bringing more Indonesians into the tax system.

"The solution is the automatic exchange of information. If there are Indonesian taxpayers who want to open a financial account in other countries, we will have the ability to access information regarding this," she said in February during the launch of a joint report on inequality by Oxfam and the International NGO Forum on Indonesia Development.

The country is expected to make its first information exchange by September 2018.

Mulyani is also planning to issue a new regulation on taxing e-commerce transactions.

In addition, she is reforming Indonesia's tax authority. Only 27 million of Indonesia's 250 million citizens are registered with the tax office, and only a million of these regularly file annual reports, according to EY. The agency is under-resourced and its staff are overworked.

In January she issued Minister of Finance Regulation No. 12/KMK.03/2017, allowing the tax authority to request access to the banking records of those it suspects as having undisclosed funds.

But, this year, tax revenues are well below target, forcing the government into an unpalatable post-amnesty climb-down by softening the rules for those who did not participate in the amnesty will be softened.

Despite the tax office having repeatedly said that unreported assets would be hunted down and tax evaders would be hit with penalties amounting to 200% of the tax owned, individuals and corporations will now only have to pay the rate of income tax (30% for individuals, 25% for corporations) if they voluntarily report their assets to the tax authority before June 2019. Critics say this is a second tax amnesty to plug gaps in the budget, but it will be the best option in the long term if it gets more Indonesians paying tax.

"There is no such thing as tax amnesty number two," Ken Dwijugiasteadi, chief of Indonesia's tax office, told a press conference on November 27, a few days before his retirement. "There was no investigation [against suspected tax evaders] during [the] tax amnesty. Presently, though, investigations [are] ongoing."

Those whose assets are found by the authorities before they self-report will still be subject to 200% penalties. So far, since the amnesty, the tax office has hit 200 taxpayers with bills totalling around $22 million.

Dwujugiasteadi was replaced on December 1 by Robert Pakpahan, who Mulyani proposed for the role and is seen as a calmer, more moderate leader for the tax office.

This is important for the way Mulyani wants to move Indonesia's taxation system forward as she seeks a cooperative relationship between government and business.

"I want to get support from all of you," Mulyani told an Indonesian Employer Association CEO gathering in Jakarta in February. "If I collect taxes, it doesn't mean I harass you, but if my subordinates harass you, report them to me."

"From the Finance Ministry side, I promise to organise ourselves and improve the institution so it can truly serve the people," she said. "We are cleaning up this side… Please, help us by cleaning up from the other side, too."

With the amnesty, and the extension of softer-touch rules until 2018 for businesses that cooperate, Mulyani is holding up her side of the bargain. The test of her success will be whether Indonesia manages to creep towards the 13% taxation to GDP ratio she has set as her target.