Former Association of Southeast Asian Nations (Asean) secretary-general Surin Pitsuwan has died in Thailand at the age of 68.
Thailand's Democrat Party said Mr Surin died in Bangkok on Thursday of a sudden heart attack.
He is a former politician from the party who also served as Thailand's foreign minister in the late 1990s under a Democrat-led government.
Mr Surin is best known for his time at the head of the 10-member Asean from 2008 until 2012. His name was also mentioned as a possible candidate for United Nations secretary-general.
He remained active in regional diplomatic circles until his death.
Mr Surin appeared to be in good health before he died. Posts on his official Facebook page show him visiting a Bangkok co-working space on Wednesday.
Two weeks ago, he spoke at a conference marking the 50th anniversary of Asean.
His remarks, punctuated with emphasis in his trademark deep voice, lauded co-operative organisations like Asean as a means of "creating a space for the region to talk to itself".
He asked: "How can we unleash the energy, the creativity, the power of 640 million people onto the platform of Asean?"
He also suggested that a new era - possibly one of less co-operation - may be emerging.
"It has been an age of multilateralism, talking to each other in a big group," he said. But, he lamented, "the era of multilateralism is disappearing".
"Be ourselves," he said of Asean nations. "Be self-sufficient. Be helpful to each other before we wait for contributions from the outside."
Thailand's Ministry of Foreign Affairs said Mr Surin "contributed greatly to the advancement and interest of Asean, as well as the promotion of Asean on the international stage. His outstanding personality, knowledge and wisdom were truly recognised by global leaders."