Every school kid who paid attention in sixth- or seventh-grade social studies or history class probably heard of Lewis and Clark, the explorers who mapped much of the land west of the Mississippi at the dawn of the 19th century. But even the most attentive student has little inkling of York, William Clark’s slave whose linguistic skills and natural diplomacy were indispensable to his master and his partner, Merriweather Lewis.

In many American history books, the story of Lewis and Clark is inseparable from President Thomas Jefferson, who assigned them the task of exploring the west after the United States had practically stolen millions of acres of land from the French during the Louisiana Purchase in 1803.

The lives of Lewis and Clark have been fairly documented but very little is known about York, who was born around 1770 or 1780, depending on the source, in Caroline County, Va. We know that he was born in slavery and had a brother and sister named Nancy and Juba. They were also slaves who belonged to Clark.

Like many privileged white boys in the South, York was Clark’s play companion but became his playmates’ property after the death of Clark’s father. There are reports that York was married, though the couple was apparently separated by 1811, when she, for undisclosed reasons, was sent to Mississippi. York was a man of great strength and athletic ability, and his physical endowment may have been significant in saving Clark’s life when he was attacked by a bear.

When Clark was commissioned by the president to take an expedition out west, York joined his master, and this was a wise choice since, time and time again, York’s ability to speak the various Native American languages they encountered was extremely important. He may have learned these languages from Sacagawea, the Shoshone maiden who also traveled with the team as an interpreter.

York was a combination scout, hunter, medicine man and diplomat during the miles of challenging travel in the trek to the Pacific Ocean. At this final destination, he also helped in the construction of the dwellings that were necessary in the often inclement weather. Being given so much latitude during the trip may have influenced York’s quest for his freedom, which he ultimately received, though, unlike the other members of the expedition, he wasn’t paid.

York’s Blackness was of endless curiosity to the Native Americans he met, many of them so intrigued by the color of his skin that they attempted to see if it could be rubbed or scrubbed off. Such a scene is marvelously captured by painter Charles Russell, with York pictured in a tribal hut among the Mandan Indians as they marveled at his physique and color. There are even stories about his sexual escapades among the Indian women, many of them eager to share their wigwams with him.

In his authoritative book “Black Indians,” noted scholar William Katz offers several pages on York and his adventures with Lewis and Clark, as well as how the Native Americans responded to him. “Those who had been brave and fearless, the victorious ones in battle, painted themselves in charcoal,” Katz writes of an explanation from a Flathead Indian about York. “So the black man, they thought, had been the bravest in the party.”

In 1832, a year after York’s death, the great writer Washington Irving, of “Sleepy Hollow” fame, interviewed Clark, who told him that he had freed York. But the long dependency adversely affected York and he, according to some reports, yearned to return to serve Clark, and there is some dispute about the accuracy of Clark’s account of York’s later years.

According to another writer, Zenas Leonard, he encountered a Black man living among the Crow Indians in 1834. The man told Leonard that he had been living in the Indian village since his days traveling with Lewis and Clark. He said he returned to Missouri with the expedition and then came back to live among the Crow. Leonard seemed convinced that this man was York given his knowledge of languages and the chronology of his narrative.

Katz’s summary on York’s liberation adds that he was given “a wagon and six horses. With these, he ran a transportation business between Nashville and Richmond. But the explorer saw his business go from bad to worse, and York eventually died of cholera.”

There are few monuments in honor of York and at least two statues capturing his magnificent physique. One of them by sculptor Ed Hamilton can be found in Louisville at the Plaza near the Ohio River. A similar likeness of him overlooks the campus, appropriately, at Lewis and Clark College in Portland, Ore. Other than some paintings depicting him in various settings among Indians, there is no true image of York’s face. Even so, he has been immortalized in an opera by composer Bruce Trinkley and librettist Jason Chamesky. In Broadwater County, Mont., a group of islands are called York’s Islands and may have been named after him.

York was posthumously granted the rank of honorary sergeant in the United States Army by President Bill Clinton in 2001. Among several books written to commemorate his contribution to the founding of the west is “Buffalo Dance: The Journey of York,” a book of poetry by Frank X. Walker in 2004, published by the University of Kentucky Press.