Maurice Ralph Hilleman (August 30, 1919 – April 11, 2005) was an American microbiologist. He specialized in vaccinology. He developed over 36 vaccines, more than any other scientist. Of the 14 vaccines currently recommended, he developed eight: those for measles, mumps, hepatitis A, hepatitis B, chickenpox, meningitis, pneumonia and Haemophilus influenza 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".

At the time of his death on April 11, 2005, at the age of 85, Hilleman was Adjunct Professor of Pediatrics at the University of Pennsylvania in Philadelphia.