Hessian Boots: In the 1790s, British Army officers wore boots called Hessians, named after German mercenaries who fought alongside the British in wars, including in the Irish Rebellion of 1798. The soldiers from the German state of Hesse were called Hessians and their boots took their name from Hesse, where they were made. The Hessian boot was made from soft, highly polished calfskin, knee high, curved top and with a V cut at the front and often had a decorative tassel.

They were shaped like a stirrup so the rider could easily insert their feet into the stirrups and the feet were kept securely in place. But tassels on Hessian boots were designed for wearing with breeches and didn’t suit tight fitting and fashionable new trousers that dandies like Beau Brummell wore in 1800s and so were replaced by Wellington Boots.
 

In 1823, the New Monthly Magazine had a comical story about tight pantaloons and Hessian boots being a perfect pairing. ‘…. tight pantaloons without Hessian boots were as preposterous as a haunch of venison without currant-jelly, or a leg of pork without peas-pudding.’
https://books2read.com/SuziLoveFashionMen1800-1819