Politician, printer, inventor, diplomat, author, scientist—Benjamin Franklin will forever be remembered as a man of many talents. But not everyone knows the founding father was also a volunteer firefighter who at age 30 established Philadelphia’s first fire department. Tom Lingenfelter, president of the Heritage Collectors’ Society in Doylestown, Pennsylvania, recently announced his discovery of a relic from this fascinating phase of Franklin’s career: a document listing his name and those of the Union Fire Company’s other members, thought to date to 1736.

Born in Boston in 1706, Franklin left home and moved to Philadelphia at age 17. His adoptive hometown still bears numerous traces of his extraordinary legacy, from the University of Pennsylvania to America’s first lending library, the Library Company of Philadelphia. One of the city’s most central and successful public figures from a very young age, Franklin cofounded the Union Fire Company, an all-volunteer brigade, in 1736....