Dr. Hennekens has emerged as one of the world's top public health researchers. He has written more than 400 articles and a medical textbook now used worldwide.

Before an English country doctor named Edward Jenner stepped forward to attack it, smallpox killed people by the thousands.

In 1616, when William Harvey announced that the heart propels blood and that blood circulates throughout the body, his findings were revolutionary.

Although genetic mutations cause just 5 to 10 percent of the more than 192,000 annual U.S. cases of breast cancer, Dr. King's discovery showed the importance of understanding how gene-linked proteins help trigger many types of breast cancer.

Recognized as a world expert on aging, neuropsychiatrist Robert Neil Butler, M.D., helped lead the drive to make "geriatrics" a formal medical discipline.

Dr. Levi Watkins Jr., M.D., who overcame discrimmination and was influenced by the Rev. Dr. Martin Luther King, Jr., became one of the country's premier cardiac surgeons. He holds a passion for humanitarian issues and racial equality -- particularly in medicine.

Vesalius revolutionized the science of anatomy by basing his findings on direct observation of the body itself, rather than on centuries-old received wisdom.