Who was the first to observe “animalcules” under the microscope?

Leeuwenhoek is universally acknowledged as the father of microbiology. He discovered both protists and bacteria. More than being the first to see this unimagined world of ‘animalcules’, he was the first even to think of looking—certainly, the first with the power to see.

A. Antonie van Leeuwenhoek