Europe's royal households and Commonwealth leaders alike praised his exceptional public service.
Joe Biden described the duke as a "heck of a guy", and all living former US presidents also sent tributes.
Pope Francis paid tribute to his "devotion to his marriage and family".
The leader of the Roman Catholic Church also noted the prince's "commitment to the education and advancement of future generations".
The spiritual leader of Tibet, the Dalai Lama, wrote to the Queen and Prince Charles, saying the Duke would be remembered for having lived a meaningful life.
President Xi Jinping of China also sent his condolences to Queen Elizabeth.
The duke, whose death was announced by Buckingham Palace on Friday, accompanied the Queen during hundreds of overseas visits.