William Lee, also known as Billy or Will Lee, was an American slave and personal assistant of George Washington. He was the only one of Washington's slaves who was freed immediately by Washington's will. Because he served by Washington's side throughout the American Revolutionary War and was sometimes depicted next to Washington in paintings, Lee was one of the most publicized African-Americans of his time.

The history of George Washington and slavery reflects Washington's changing attitude toward the ownership of human beings. The preeminent Founding Father of the United States and a hereditary slaveowner, Washington became increasingly uneasy with it. Slavery was then a longstanding institution dating back over a century in Virginia where he lived; it was also longstanding in other American colonies and in world history. Washington's will immediately freed one of his slaves, and required his remaining 123 slaves to serve his wife and be freed no later than her death, so they ultimately became free one year after his own death.