Carolyn Widney "Carol" Greider (born April 15, 1961) is an American molecular biologist. She is a Bloomberg Distinguished Professor, Daniel Nathans Professor and Director of Molecular Biology and Genetics at Johns Hopkins University. She discovered the enzyme telomerase in 1984, when she was a graduate student of Elizabeth Blackburn at the University of California, Berkeley. Greider pioneered research on the structure of telomeres, the ends of the chromosomes.