A Dutch cloth merchant was the first person to see bacteria.
Antonie van Leeuwenhoek ground his own powerful lenses and in the 1670s described tiny living "animalcules" in water and scrapings from teeth, in letters to the Royal Society.
Why it matters: Microbiology — and later germ theory and antibiotics — began with his curiosity.
Letters to the Royal Society — Antonie van Leeuwenhoek (1676) Letter of 9 October 1676
Looking at cork through his microscope, Robert Hooke saw tiny box-like spaces that reminded him of small rooms, and called them cells. He published his drawings in 1665.
Why it matters: We now know every living thing is made of cells — the starting point of biology and medicine.
Micrographia — Robert Hooke (1665) Observation XVIII
The instructions for every living thing are written in a twisted ladder.
In 1953 Watson and Crick published the double-helix structure of DNA, built on X-ray images by Rosalind Franklin and Raymond Gosling, including the famous Photo 51.
Why it matters: Understanding DNA led to genetic testing, new medicines and forensic science.
Molecular Structure of Nucleic Acids — James Watson and Francis Crick (1953) Nature, vol. 171, 25 April 1953