William Sydenham (1615–1661) was a Cromwellian soldier; and the eldest brother of Thomas Sydenham. He fought for Parliament and defeated the Royalists in various skirmishes in Dorset. He was member of the various parliaments of the Commonwealth, avowal conservative principles, and defended the liberties of Englishmen. In 1654 made councillor and commissioner of the treasury by Oliver Cromwell. Took the side of the army against Parliament. In 1660, after the Protectorate, and before the Restoration, he was expelled from the Long Parliament. After the Restoration, he was perpetually incapacitated from holding office by the Indemnity and Oblivion Act.[1]