The residents of Sleepy Hollow believed the Headless Horseman to have been a Hessian. The Hessians were soldiers from Northern Germany who were rented from German princes to fight for the British in the Revolutionary War. Although six German princes rented out their troops to the British, the Hessians, from Hesse-Kassel in Hesse, were the most numerous and most important, making up about 17,000 of the 30,000 total troops sent.
The German princes had done this before, and they had no particular qualms about whom they rented the men to, although the British were generally their best customers. During the Revolutionary War, the Germans still saw rebellion as a heinous crime, so no princes sided with the colonialists. The British were ambivalent about using the Hessians, with some claiming it would be much cheaper than recruiting and training their own men--and they would be able to quickly quell the rebellion. Others worried that the Hessians, being far from home and fighting without a personal stake in the overall outcome, would be tempted to desert, or that the Americans, seeing that the British had bought in or brought in foreign troops, would do the same. In the end, though, the British decided to use them, and hired German soldiers made up about a quarter of the total forces sent to America.
The quality of the Hessians varied greatly. They were largely conscripted soldiers, or even prisoners, and they made very little money as compared to the officers. They thus were not excited about going all the way to America to fight a war that had nothing to do with them, and for which they were compensated little. Many of them had good training, however, certainly in higher proportion than the rebel soldiers, and many of them were distinguished by the quality of their skills.
The first Hessians arrived on Staten Island in August of 1776, and the first battle they fought in was the Battle of Long Island. Throughout the rest of the war, Hessians were involved in almost every battle. The presence of the Hessians deeply offended those colonialists who had been against rebelling—they considered themselves British subjects, and they were greatly offended that the British would use foreign troops against them. Americans also tried to take advantage of the Hessians’ unhappiness, trying to convince them to desert. In the end, most of the Hessians returned home, but about five thousand did stay and settle in America or Canada.
Sleepy Hollow and the older men had reasonably fresh memories of the war. The ghost of a Hessian was doubly scary, for not only was it a ghost but also it was the ghost of someone who had been hired to kill rebellious Americans. And this particular Hessian was likely to be particularly angry for having died while in service.