James Harrison, 74, has an antibody in his plasma that stops babies dying from Rhesus disease, a form of severe anaemia.
Mr Harrison has been giving blood every few weeks since he was 18 years old and has now racked up a total of 984 donations.
Just after he started donating he was found to have the rare and life-saving antibody in his blood.
At the time, thousands of babies in Australia were dying each year of Rhesus disease. Other newborns suffered permanent brain damage because of the condition.
The disease creates an incompatibility between the mother's blood and her unborn baby's blood. It stems from one having Rh-positive blood and the other Rh-negative.
Mr Harrison is Rh-negative and was given injections of Rh-positive blood.
It was found his plasma could treat the condition and since then it has been given to hundreds of thousands of women.
It has also been given to babies after they are born to stop them developing the disease.
It is estimated he has helped save 2.2 million babies so far.
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