Ban, a South Korean politician who served 10 years as the eighth secretary general of the U.N. until 2017, has been a vocal proponent of other progressive causes like climate change and LGBTQ rights.
"While swearing in as secretary general, I pledged I would make this world better for all," he said. "Nobody would imagine that there should be so many people – 30 million people – who would be left behind" in the U.S.