Anton van Leeuwenhoek
As a draper's assistant, one of his jobs was to examine cloth through a magnifying glass. During one his experiments with lenses, he found a way of grinding them to make them more powerful. And in 1676, he invented a single lens microscope.
With his new microscope, he studied minute forms of life. Leeuwenhoek was the first human to observe singled-celled animals with microscope. He called the microscopic world "animalcules", or "little animals", what we call today microbes. But then, Leeuwenhoek didn't know what they were or that they were linked to horrible diseases.
Anton van Leeuwenhoek's lenses made microscopic study possible. His accurate descriptions of microbes formed the basis of later medical and biological research.