Bacteria and microorganisms were first observed by Anton van Leeuwenhoek in 1676 using a single-lens microscope made by himself. He is known as the Father of Microbiology and thus is known as the first microbiologist. He described the first organisms he saw as animalcules. He was a Dutch tradesman. He was an amateur scientist, though his discoveries were of top quality and created a new discipline in biology. He published his discoveries through the English Royal Society.
Ferdinand Cohn founded the new field of bacteriology, currently a subdiscipline of biology. He was the first to propose a taxonomic classification of bacteria.
Pasteur (1822-1895) and Koch (1843-1910)
Louis Pasteur along with Robert Koch are the founders of medical microbiology. Pasteur proved the Theory of Spontaneous Generation to be wrong. He invented a method for food preservation called pasteurization and vaccines against diseases such as antrax, fowl cholera and rabies. Koch is the author of the Germ Theory of Disease which states that specific diseases are caused by microorganisms. He discovered including Mycobacterium tuberculosis, the causing agent of tuberculosis.
Beijerinck (1851–1931) and Sergei Winogradsky (1856–1953)
They are the founders of general microbiology. Beijerinck discovered viruses. Winogradsky discovered the concept of chemolithotrophy and nitrifying and nitrogen-fixing bacteria.