The credit for introducing the word "cell" to biology goes to Robert Hooke.

In 1665, Hooke observed thin slices of cork under a microscope. He noticed small, box-like compartments that reminded him of the cells monks lived in, and he named these compartments "cells."

While Hooke didn't actually see living cells (he was looking at the dead cell walls of cork), his observations were crucial in laying the groundwork for the development of cell theory.