The man who first saw the invisible world wasn't a scientist by trade. He sold cloth.

Antonie van Leeuwenhoek was born on October 24, 1632, in Delft, in the Dutch Republic. Working as a draper, he learned to grind tiny glass lenses and built single-lens microscopes that were the most powerful of their era.

Peering at pond water, blood, insects and even the plaque on teeth, he described living things no one had ever seen. For decades he sent about 300 letters to the Royal Society of London, which published his findings.

Why it still matters: he is often called the father of microbiology, and every lab test that looks for bacteria traces back to his curiosity.

What everyday thing would you most want to see under a microscope?

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