Thomas Stanley, 1st earl of Derby b. c. 1435 d. July 29, 1504, Lathom, Lancashire, Eng.

Also called (1459-85) 2ND BARON STANLEY, a prominent figure in the later stage of England's Wars of the Roses. Great-grandson of Sir John Stanley (d. c. 1414), who created the fortunes of the Stanley family, Thomas Stanley began his career as a squire to King Henry VI in 1454. At the Battle of Blore Heath in August 1459, Stanley, though close at hand with a large force, did not join the royal army, while his brother William fought openly for York. In 1461 Stanley was made chief justice of Cheshire by Edward IV, but 10 years later he sided with his brother-in-law Warwick in the Lancastrian restoration. Nevertheless, after Warwick's fall, Edward IV made Stanley steward of his household. About 1482 he married, as his second wife, Margaret Beaufort, mother of the exiled Henry Tudor (the future Henry VII). Stanley was one of the executors of Edward IV and was at first loyal to the young king Edward V. However, he acquiesced in Richard III's accession and retained his office as steward,avoiding entanglement in the rebellion (1483) on behalf of Henry Tudor in which his wife was deeply involved.

He was made constable of England and was granted possession of his wife's estates with a charge to keep her safe in some secret place at home. Richard III could not well afford to quarrel with so powerful a noble, but he became suspicious when, early in 1485, Stanley asked leave to retire to his estates in Lancashire, and in the summer Richard asked Stanley to send his son Lord Strange to court as a hostage. After Henry Tudor had landed, Stanley made excuses for not joining the King. On the morning of Bosworth (August 22), when Richard summoned Stanley to join him, he received an evasive reply and thereupon ordered Lord Strange to be executed, although his order was neglected and Strange escaped. After the Battle of Bosworth Field, Stanley, who had taken no part in the fighting, placed the crown on Henry's head. Henry VII confirmed him in all his offices and created him earl of Derby. His son Thomas succeeded him as 2nd earl of Derby.

I found this info at britannica.com