By Natasha Gruneberg
The director-general of the World Health Organization (WHO), Dr Lee Jong-wook, has died at the age of 61.
Dr Lee had been director-general since 2003
He had worked for the agency for more than 20 years and was the first South Korean to head a United Nations agency.
Dr Lee studied medicine at Seoul National University and received a Master of Public Health degree from the University of Hawaii.
Before joining WHO, he worked for two years at the LBJ Tropical Medical Centre in American Samoa.
He worked at the WHO for more than 20 years at a regional level and at the organisation's headquarters, in technical, managerial and policy positions.
He began his work there as an advisor on leprosy, and among his later responsibilities were fighting tuberculosis and promoting the vaccination of children against preventable diseases.
Bird flu response
Dr Lee headed the WHO's Global Programme for Vaccines and Immunizations and in 2000 became the leader of its Stop TB programme.
His original intention had been to improve international monitoring to help tackle outbreaks of diseases like Sars (Severe Acute Respiratory Syndrome) and to fight HIV/Aids, especially in poorer countries.
The WHO flag was flown at half-mast at the headquarters in Geneva
But the two years he spent in office were dominated by the spread of bird flu, or avian influenza, through Asia, Europe and Africa.
Under Dr Lee's leadership, the WHO has been co-ordinating the global response to human cases of the H5N1 strain of bird flu and monitoring the threat of an influenza pandemic, in case the virus should mutate into a strain easily spread among people.
Dr Lee's election to the post of director-general was to have been for a five-year term but was cut short when he was taken ill suddenly during an official engagement.
He underwent surgery for a blood clot to the brain but did not recover.
He was known as a warm, friendly man, who lightened the mood at press conferences with jokes.
He is survived by a wife and son.