Sir John Cockayne (died 1438) was an English soldier, politician and landowner whose wealth made him a major force in the affairs of Derbyshire under the House of Lancaster. After numerous acts of criminality in concert with other Midlands landowners, he became a member of the Lancastrian affinity centred on John of Gaunt and a supporter of Henry IV. He fought in two campaigns of the Hundred Years War but his violence and lawlessness continued and he was decidedly out of favour during the reign of Henry V. With power less concentrated in the early years of Henry VI, he was able to serve three terms as High Sheriff of Nottinghamshire, Derbyshire and the Royal Forests and to wield considerable power and influence. He represented Derbyshire no less than nine times and Warwickshire twice in th