While he didn't actually discover cells, he was the first to observe and describe them in 1665. He examined thin slices of cork under a microscope and observed small compartments that he named "cells" due to their resemblance to the cells of a monastery.

However, it's important to note that Hooke observed the cell walls of dead plant cells, not the living cells themselves. The discovery of living cells is attributed to Anton van Leeuwenhoek, who in the late 1600s used his improved microscopes to observe living organisms like bacteria, protozoa, and red blood cells.