John Graunt was a shopkeeper in 17th-century London who followed his own curiosity to a rather grand result. His work gave rise to the fields of demography and epidemiology.
Research:

Sara Weiss’s Journeys to the Planet Mars
39:45

SYMHC Classics: Charles Colchester
33:49

Behind the Scenes Minis: Lager, Ale, Emo Girl
25:06