Waller, Sir William, 1597–1668, English parliamentary general. He fought (1620–22) in the Thirty Years War and was knighted in 1622. A zealous Puritan, he sat in the Long Parliament (see English civil war), became a colonel in the parliamentary army, and achieved a series of victories that gained him the popular title of William the Conqueror. In 1643, however, he was defeated by the royalists at Roundway Down. He received fresh troops and continued campaigning with mixed results until the creation of the New Model Army (which he had originally proposed). The Self-Denying Ordinance (1645) prohibited his serving in that army because he was a member of Parliament. A leader of the Presbyterian party in Parliament, he was imprisoned (1648–51) by the army and again under the Protectorate. He promoted the return of Charles II and was returned (1660) to Parliament by General Monck's influence, but after the Restoration he retired.