The inventor of the 5th Avenue candy bar was William H. Luden, the developer of the famous Luden cough drop. Luden launched a backroom candy business in 1879 in the rear of his father’s jewelry shop in Reading, Berks County. In 1936, William Luden created the 5th Avenue candy bar. Its name can be traced to H. Earl Erb, Luden’s secretary-treasurer who helped develop the bar and who lived at the corner of Fifth Avenue and Chestnut Street, West Reading.
The original version of the 5th Avenue bar had roasted peanuts, crushed molasses, milk chocolate, and was topped with toasted almonds. It has been suspected that production was greatest during the World War II era because 5th Avenue bars kept well and were given out to the troops.
Today, 5th Avenue candy bars are manufactured by The Hershey Company.

For a Philadelphia area connection,  Luden was buried in West Laurel Hill Cemetery, Bala Cynwyd, PA

This link connects to a very thorough history of the company and its industrial buildings. It covers the two mansions he built in Reading that still exist.
https://goreadingberks.com/william-h-luden-ludens-candy/

It also features a video showing candy production.
Luden’s 100th