York (c. 1770– March 1831) was the only one of the Lewis and Clark Expedition to serve without choice in the matter: he was William Clark's slave, having been inherited from Clark's father. He was about the same age as Clark and had been his companion from childhood, as was common in the South at the time. The journals present him as a large, strong man, who carried a gun and shared the duties and risks of the expedition in full. Wikipedia
The definitive Wikipedia entry for York. Wikipedia is the biggest multilingual free-content encyclopedia on the Internet. en.wikipedia.org/wiki/York_%28Lewis_and_Clark%29