While many scientists contributed to the understanding of bacteria, the first person to observe and describe bacteria was Antonie van Leeuwenhoek in the 17th century.

He used a simple microscope he built himself to examine pond water, rainwater, and scrapings from his teeth. He was astonished to see tiny creatures moving around, which he called "animalcules". Though he did not understand what these creatures were, his detailed observations and descriptions laid the groundwork for future studies on microorganisms.