York was the name of the black servant who accompanied Captain William Clark on the famous Lewis and Clark Expedition to the Pacific Ocean and back in 1803-1806. He was given to William Clark by Clark's father and was roughly the same age as Clark.
York, who's first name was rumored to be Ben, astonished the Indians that the expedition encountered. Few had ever seen a black man before, and he was the subject of much interest. He was known as a practical joker and on more than one occasion took advantage of the Indians' fear of him by telling them that he was a wild man and ate children. Stories of his sexual prowess and conquests among the Indian women didn't surface until 1814, when an interview with Clark was exaggerated greatly.
From the expedition's journals, it appears that York functioned as a full member of the expedition, rather than just as a man-servant to Clark. Two geographic features were even named after him: York's 8 Islands and York's Dry River.
Upon return from the expedition, York again resumed his role as William Clark's personal slave. York asked Clark repeatedly for his freedom, or to be allowed to hire out, in order to be closer to his wife, who had a different owner, but Clark refused until at least 1816, when he finally granted York his freedom. York then opened a freighting company in Kentucky and Tennessee. He died of cholera sometime before 1832.