Antonie van Leeuwenhoek is widely regarded as the first person to observe bacteria, making him the earliest discovered and described microorganisms in the 17th century. He built and used simple single-lens microscopes to view and sketch "animalcules," which included bacteria, protozoa, and other microscopic life. His microscopic observations, dating to the 1670s and early 1680s, laid the foundations for microbiology and earned him the title often given as the “father of microbiology.”