Thomas Stanley, 1st Earl of Derby

Thomas Stanley, 1st Earl of Derby, KG (1435 – 29 July 1504) was an English nobleman. He was the stepfather of King Henry VII of England. He was the eldest son of Thomas Stanley, 1st Baron Stanley and Joan Goushill.

A landed magnate of immense wealth and power, particularly across the northwest of England where his authority went almost unchallenged, Stanley managed to remain in favour with successive kings throughout the Wars of the Roses, including King Richard III of England, who took Stanley's son as a hostage. Thomas Stanley took the side of Henry Tudor at the Battle of Bosworth in 1485. His estates included what is now Tatton Park in Cheshire, Lathom House in Lancashire, and Derby House in the City of London, now the site of the College of Arms.

Although the king for the early part of his career, Henry VI, was head of the House of Lancaster, Stanley's marriage to Eleanor, daughter of Richard Neville, 5th Earl of Salisbury (a descendant of Edward III) and sister of Richard Neville, Earl of Warwick ('Warwick the Kingmaker') in the late 1450s constituted a powerful alliance with the House of York. This did him no harm, however, even after Warwick was toppled from power, and in 1472, with the House of York again occupying the English throne, he married his second wife Lady Margaret Beaufort, whose son, Henry Tudor, was the leading Lancastrian claimant. He was the last to use the style 'King of Mann', his successors opting for the safer 'Lord of Mann'. Among his notable close relatives were his brother Sir William Stanley and his nephews Sir John Savage and Thomas Savage, Archbishop of York.