Lord Petersham was famous not only for his hat but is also the namesake of several other items of fashion including:
Bible, G. W., Bible, D. P. (1896). Pocket Dictionary of Dry-goods, Etc. United States: Trade Printing and Publishing Company.
According to a more modern costume dictionary, there was also the Petersham Cossacks (a man’s loose Cossack flaring around the ankles) and the Petersham frock coat (a man’s double breasted coat with velvet collar, lapes, and cuffs, with large flap hip pockets). Lewandowski, E. J. (2011). The Complete Costume Dictionary. United Kingdom: Scarecrow Press.
In addition to the Cossack trousers (nipped in waists and ankles, balloon legs, similar to a style popular today), he also styled himself in one shade of brown and was known for his tendency to collect items (Eccentrics of the Regency Period Series: Charles Stanhope, Lord Petersham | Every Woman Dreams… (reginajeffers.blog)). He was such a trendsetter, Prinny was known to ape his style and the two were friends.
Petersham eventually became the Earl of Stanhope and then married Maria Foote, who was a younger Covent Garden actress. The couple had two children.