While the invention of the microscope is attributed to Zacharias Janssen in the late 16th century, it was Anton van Leeuwenhoek who is credited with being the first person to use a simple microscope to observe and describe microscopic organisms.

Leeuwenhoek, a Dutch draper and amateur scientist, developed his own powerful microscopes, achieving magnifications far greater than previous microscopes. He used these microscopes to observe a wide variety of specimens, including water, blood, and even his own teeth.

In 1674, he wrote to the Royal Society of London describing his observations of tiny, moving creatures in pond water, which he called "animalcules." This discovery revolutionized our understanding of the microscopic world and laid the foundation for the field of microbiology.