United Nations, June 13 : UN Secretary-General Antonio Guterres on Saturday expressed his sadness over the death of William Swing, a former leader of the UN migration agency. "I am deeply saddened to learn of the passing of my dear friend William Swing, the former director-general of the International Organization for Migration (IOM) and past leader of the UN peacekeeping mission in the Democratic Republic of the Congo," he said in a statement, Xinhua reported. "A true humanist, Bill Swing dedicated his life to serving the most vulnerable of the vulnerable in our world. I will never forget his dedication and compassion as we worked together side by side in the face of some of the worst displacement crises," he said. "To his wife, his family and his former colleagues, I send my deepest condolences and profound solidarity." Swing, an American diplomat who had served as US ambassador to various countries, died on Saturday at the age of 86. He was IOM director-general between 2008 and 2018. /IANS