English mason. He worked at Eton College in the 1450s, Tatter-shall Church, Lincs., in 1478, and around the same time built Kirby Muxloe Castle, Leics., where the resident mason or clerk of the works was Robert Steynforth (fl. 1480s). Cowper may also have been responsible for the gatehouse-tower at Esher, Surrey (c. 1475–80), the school at Wainfleet, Lincs. (1484), and the great tower at the Bishop's Palace, Buckden, Hunts. (also 1480s). Cowper is important in the development of Tudor brickbuilt architecture which was to become fashionable. He appears to have finished his career in the service of King James IV of Scotland (1488–1513), for a John Cowper was in charge of the works at Rothesay Castle, Bute, in 1512, where he was paid handsomely, so must have enjoyed considerable status.
J. Harvey (1987)