York was Clark's slave.  He also went along on the expedition.  The Mandans and Hidatsas thought he had great medicines.  The Native Americans thought that he was a white man painted black so he let them rub his skin to make sure.  He would dance for entertainment when there was a special occasion or they felt like celebrating.  York and Sacagawea had a common bond. They were the only "different" members of the exploring party.
 
 

Sacagawea
Alana J. White
1997