Maurice Ralph Hilleman was an American microbiologist who specialized in vaccinology and developed over 36 vaccines, more than any other scientist. Of the 14 vaccines routinely recommended in current vaccine schedules, he developed eight: those for measles, mumps, hepatitis A, hepatitis B, chickenpox, meningitis, pneumonia and Haemophilus influenzae bacteria. He also played a role in the discovery of the cold-producing adenoviruses, the hepatitis viruses, and the cancer-causing virus SV40.
He is credited with saving more lives than any other medical scientist of the 20th century. Robert Gallo described him as "the most successful vaccinologist in history".