Answer:
Anton Van Leeuwenhoek was the first man to witness, describe, and publish data on live cells, protozoa, amoeba, and bacteria. To accomplish this, he used simple microscopes that he had crafted.
Related Information:
He seems to have been inspired to take a disciplined approach to microscopy by having seen a copy of Robert Hooke's illustrated book, Micrographia. This publication depicted Hooke's own observations using the compound instrument that he invented. This book was very popular at the time.
While not the inventor of the microscope, Leeuwenhoek's simple microscopes certainly made significant improvements to the technololgy, especially in the shaping and grinding of the lenses. The capability of one of his single lenses, far exceeded that of Hook's instrument.
He is known to have made more than 500 microscopes, of which fewer than ten survive today.