From "Black Patriots of the American Revolution" by David Barton: James Armistead (Lafayette) (1760-1832)

James Armistead was one of the most important American spies during the Revolution. As a slave in Virginia, he witnessed much of the War; and following the British siege of Richmond in 1781, he asked his master, William Armistead, for permission to serve in the cause of American independence with General Marquis de Lafayette, a young Frenchman who came to fight with the Americans. His master agreed, and Lafayette accepted his services. Lafayette dispatched Armistead to the camp of the patriot-turned-traitor, Benedict Arnold (then a British general), to pose as an escaped slave looking for work. Arnold accepted Armistead and allowed him to work in the camp, thus placing him around other British generals, including British commander-in-chief Lord Cornwallis. Armistead obtained much vital information about British plans and troop movements, which he daily sent to General Lafayette. Ironically, Lord Cornwallis so trusted Armistead that he even asked him to become a British spy to watch the Americans. Armistead agreed and thus became a double-spy, feeding accurate information to the Americans and inaccurate information to the British. Upon learning that the British fleet was moving Cornwallis and his troops to Yorktown, Armistead quickly relayed that information to Lafayette and Washington, who gathered the American forces at Yorktown. After the British troops had landed and the British fleet had unsuspectingly departed from Chesapeake Bay, the Americans engaged the British while the French fleet blockaded the Bay to keep the British navy from returning. The Battle of Yorktown ensued, and the British – without their navy to provide reinforcements or supplies and with no way to retreat off the peninsula on which they were trapped – finally surrendered. Armistead’s crucial information had helped bring a victorious end to the American Revolution.
Following the War, Armistead returned to slavery on his master’s plantation. Three years later, in 1784, General Lafayette returned to America for a visit and met with his friend, Armistead. Lafayette penned a certificate to Virginia leaders praising the work and important contributions of Armistead. Armistead then petitioned the legislature for his freedom, which was granted on New Year’s Day, 1787. (In his latter years, Armistead also received a retirement pension from the State for his military services.) Following his emancipation, Armistead adopted the name Lafayette and thereafter called himself James Lafayette. He remained in the State as a farmer.
General Lafayette became an ardent foe of slavery both in America and in Europe, and it is believed that it was his association with James Armistead that helped clarify his views on slavery, leading him to begin his strong public crusade against that evil.
In 1824, General Lafayette made his final visit to America; his tour across the nation was greeted by crowds of thousands in city after city. When touring Richmond, the General recognized in the crowd his black comrade from four decades earlier (now an old man) and called him out by name and embraced him – the last time the two patriot friends were to meet.