Paul Wolfowitz was always a controversial choice to head the World Bank. He was said to be too closely identified with the Bush Administration’s Iraq policies and, in particular, with its ambitions to bring about a democratic transformation in the Middle East, to give the bank credibly independent leadership. He was said to lack sufficient knowledge of international banking, and of the challenges of economic development.

Some of this criticism was motivated by antagonism to the so-called “neocon agenda”, and had more to do with a generalised antipathy to the Bush Administration than with the effective running of the world’s biggest development lender. No Bush nominee would have had an easy ride, and Mr Wolfowitz’s diplomatic career, intellectual abilities and penchant for questioning conventional thinking made him a potentially powerful agent for change. In the two years he has spent at the bank’s helm, Mr Wolfowitz has done much to prove the critics wrong.

The first of the World Bank’s ten presidents actually to have lived in a developing country, as US Ambassador to Indo-nesia where he championed the cause of accountability and political reform, Mr Wolfowitz brought to the job a passion for the economic betterment of the poor, the ability to ask the right questions and a proper impatience with aid failures.

He has been very much his own man, publicly taking Washington to task on aid policy and over the flagging Doha Round of trade negotiations. More importantly, his admirably persistent campaign against the corrupt use of development aid — by government officials siphoning off aid, by private contractors colluding with them and by World Bank personnel — took on vested interests across the global development industry. The drive for probity made him unpopular not just with governments and companies which saw funds cut off but also, indefensibly, with the British Government, whose concern ought to be that taxpayers’ money actually reaches and helps those it is intended to benefit. He was forced by the World Bank board to compromise, but even in watered-down form, the anticorruption rules finally accepted last month set new international standards for holding those who misuse or misappropriate aid to account. The world’s poor are in his debt.

To safeguard the credibility of the reforms for which he fought, Mr Wolfowitz must hold himself to those same standards. It has emerged that he personally ordered a promotion and a $61,000 pay rise for Shaha Riza, a Libyan-born bank employee who is also his partner, to compensate for her involuntary secondment to the US State Department. Ms Riza was moved, to forestall a conflict of interest, after Mr Wolfowitz disclosed the relationship to the bank’s board. He would have preferred her to stay, recusing himself from all decisions involving her. By the same token, when the bank’s ethics committee insisted on her transfer, he should, as he now admits, have “kept myself out of the negotiations”.

Opponents of his reforms will exult in his fall. “In the larger scheme of things,” he has said, the bank “has much more important work to focus on.” It is by resigning that he will now best assist it to do so.