Jim Yong Kim, the Korean-American president of the World Bank Group, has unexpectedly resigned his post. His resignation takes effect on Feb. 1.

In a tweet announcing his resignation as the bank's 12th president, Kim said "I will be stepping down as @worldbank Group president on February 1. It's been the greatest privilege I could have ever imagined to lead the dedicated staff of this great institution to bring us closer to a world that is finally free of poverty."

In a follow-up statement, Kim said it has been a great honor "to serve as President of this remarkable institution, full of passionate individuals dedicated to the mission of ending extreme poverty in our lifetime.

"The work of the World Bank Group is more important now than ever as the aspirations of the poor rise all over the world, and problems like climate change, pandemics, famine, and refugees continue to grow in both their scale and complexity."

Kim,59, resigns two years ahead of his scheduled departure at the end of 2021. Kim has not made public the exact reason for his premature exit.

What is known is that Kim will join a firm focusing on infrastructure investments in the developing world and return to the board of Partners In Health (PIH), the health organization he co-founded in 1987 along with Paul Farmer, Todd McCormack, Thomas J. White, and Ophelia Dahl.

PIH gained fame for radical new, community-focused health care programs in Haiti, which executed treatments based on local needs and by training community members to implement them. PIH currently employs more than 13,000 people in 12 countries. Kim left PIH as Executive Director in 2003.

Kim is the first World Bank president whose professional background is not in the political or financial sectors. He is also the first to have previous experience personally tackling health issues in developing countries, which explains his affinity for helping the poor.

He was appointed World Bank president in 2012 and was re-appointed president in 2015. Kim shifted the focus of the bank to attract private-sector investment in development projects.

By tradition, the president of the United States nominates the president of the World Bank. As a consequence, all World Bank presidents since the bank's founding in 1944 have been Americans. Former President Barack Obama appointed Kim as World Bank president in March 2012.

President Donald Trump will appoint Kim's successor. There is no clear frontrunner for the post, and Washington pundits fear Trump might appoint someone who will antagonize the developing world.