* Robert Hooke (1665): He was the first to observe and name cells. He examined a thin slice of cork under a microscope and noticed small, box-like compartments which he called "cells" because they reminded him of the cells of a monastery.

* Matthias Schleiden (1838): He concluded that all plants are made of cells.

* Theodor Schwann (1839): He extended Schleiden's findings to animals, concluding that all animals are made of cells.

Therefore, the cell theory is attributed to the combined contributions of Hooke, Schleiden, and Schwann.