For the former governor of Mississippi, see Bill Waller.
Sir William Waller (c. 1597 - September 19, 1668), was an English soldier during the English Civil War. He received his education at Magdalen Hall, Oxford, and served in the Venetian army and in the Thirty Years' War. He received a knighthood in 1622 after taking part in Vere's expedition to the Palatinate.

Election to Parliament and early military career
By this time the confusion in all the armed forces of the parliament had reached such a height that reforms were at last taken in hand. The original suggestion of the celebrated "New Model Army" came from Waller, who wrote to the Committee of Both Kingdoms (2 July 1644) to the effect that "an army compounded of these men will never go through with your service, and till you have an army merely your own that you may command, it is in a manner impossible to do anything of importance."
Simultaneously with the New Model came the Self-denying Ordinance, which required all members of parliament to lay down their military commands. Waller did so gladly - the more as he had already requested to be relieved - and his active military career came to an end. But the events of 1643 - 1644 had done more than embitter him. They had combined with his Presbyterianism to make him intolerant of all that he conceived to be licence in church, state or army, and after he ceased to exercise command himself he was constantly engaged, in and out of parliament, in opposing the Independents and the army politicians, and supporting the cause of his own religious system, and later that of the Presbyterian-Royalist opposition to the Commonwealth and Protectorate régime. He was several times imprisoned between 1648 and 1659.