When Dr Lee Jong-wook took over the reins of the World Health Organisation he made HIV his number one target.
Lee Jong-wook was appointed in 2003
Soon after his appointment in January 2003, he launched the Three by Five programme.
The plan was to get 3m people in the poorest parts of the world on to HIV drugs by the end of 2005.
The exact figure currently receiving drugs is not known, although estimates put it at little over 1m.
The failure led to public apologies by WHO officials. But many argue this should not cloud the strong leadership shown by Dr Lee in the last two years.
The target was always acknowledged to be very ambitious and in some ways the failings were out of his hands.
He successfully lobbied western governments for extra funding, but treatments often struggled to reach people with HIV because of a lack of co-ordination on the ground by some countries.
Aids campaigners said his intervention has done much to galvanise the drive to improve access to treatment.
Nick Partridge, chief executive of Terrence Higgins Trust, said: "Dr Lee Jong-Wook has made an important contribution.
"The Three by Five goal meant that for the first time, there was a real target for making HIV treatment available to people from very poor countries.
"It broke the deadlock with those who said it just couldn't be done, and this was hugely important for a great many people who would have died without it."
"There is a need for greater commitment from governments and pharmaceutical companies to making anti-retroviral drugs widely available, and also for new prevention methods such as a vaccine to prevent the millions of new infections which are taking place every year."
The South Korean also led the fight against TB and polio - both of which he had championed in his previous roles at the WHO.
He has been instrumental in the push to eradicate polio. The virus is only endemic in India, Nigeria, Pakistan and Afghanistan after a mass immunisation campaign was launched in the late 1980s.
Lee Jong-wook has campaigned for better access to drugs
The target to eradicate it by the end of last year failed - partly due to funding problems - but experts say doctors are closing in on the goal.
Just last month WHO announced it was launching one of its most demanding immunisations programmes by targeting 16m children in remote areas of Afghanistan and Pakistan.
On TB, Dr Lee already had a good track record.
As one of the architects of the Global Partnership to Stop TB, a complex partnership of more than 250 governments, businesses and charities, he had helped to create more accessible treatment programmes.
However, this has been marred by the rises in cases that have been seen in recent years.
The WHO responded by announcing earlier this year that millions of pounds of extra funding, much of which has been donated by Microsoft boss Bill Gates, will be spend on developing a new drug and vaccine for TB.
Unsurprisingly, the tributes have already started flooding in. UN secretary general Kofi Annan described him as a "great man".
But perhaps the judgements should wait. His lasting legacy may well hang on how the world copes with a flu pandemic.
Under Dr Lee's tenure, the WHO has been quick to warn of the danger posed by the bird flu virus mutating with a human version.
The warnings have prompted governments to start making preparations, but only time will tell if they are sufficient.