Robert Hooke is credited as the scientist who first discovered cells. He examined a slice of cork under a microscope and found empty spaces enclosed by walls. He called these structures pores, and the term cell later stuck as being synonymous with what he had seen.
The realization that cells were the building blocks of life took place around 1665. In addition to Hooke, several other scientists are credited for examining cells around this time. While Hooke used a deceased plant to further his studies of the cell, Dutch scientist Anton Van Leeuwenhoek used live specimens to examine cell structure.