Former South Korean Prime Minister Lee Hae-chan, a veteran politician and democracy activist, died at age 73 during an official visit to Ho Chi Minh City, Vietnam, after suffering a heart attack.

Lee, who served as prime minister from 2004 to 2006 and was a seven-term parliamentarian, began his political career as a student activist jailed in the 1970s for pro-democracy efforts.

Known as a shrewd strategist and often a firebrand, he supported four liberal presidents, including the current leader, and was influential in shaping South Korea’s modern democracy.

His death prompted condolences from South Korean President Lee Jae Myung, the opposition People Power Party, and Vietnamese leaders, who tried to provide emergency care, US News has World Report has reported.

Lee had been in Vietnam to chair the Peaceful Unification Advisory Council, advising the government on policy toward North Korea.