Northumberland, Algernon Percy, 10th earl of (nôrthŭmˈbərlənd) [key], 1602–68, English nobleman. He was created Baron Percy in 1626 and succeeded his father as earl in 1632. Charles I in 1638 made him lord high admiral of England and in 1639 gave him command of the expedition against Scotland, which he was forced to relinquish because of illness. Disagreeing with the king's policy, he gradually moved over to the parliamentary party. His support gave Parliament an important advantage, for it thus gained control of most of the fleet. Northumberland, a leader of the peace party, twice engaged in unsuccessful negotiations with Charles on behalf of Parliament, opposed the king's trial, and was given custody of the king's younger children. He took no active part in affairs under the Commonwealth or after the Restoration, although he held several offices after 1660.