The Royal House of Lancaster was founded by the second son of Henry III, Edmund Crouchback, 1245-96, who was created earl of Lancaster in 1267. Earlier (1254) the prince had been made titular king of Sicily when the pope offered that crown to Henry III in order to keep Sicily and the Holy Roman Empire separated. However, the English barons refused financial support for the Sicilian wars, and the title was withdrawn (1258). Later Edmund fought for his brother, Edward I, in Wales and Gascony. His nickname “Crouchback,” or crossed back, refers only to the fact that he went on crusade to Palestine in 1271 and, hence, was entitled to wear the cross.

After Edmund married Blanche of Artois, he adopted her symbol the Provins rose (named after a town in Champagne), which she herself had adopted from her first husband, Henry of Champagne. Thus, the origin of the Lancastrian red rose was thoroughly French.

Edmund's son Thomas, Earl of Lancaster, 1277?-1322, led the baronial opposition to his cousin Edward II . He was one of the lords ordainers and from 1314 to 1318 was virtual ruler of England. He tried unsuccessfully to drive the Despensers (see Hugh le Despenser) from England, was defeated at the battle of Boroughbridge, and was beheaded for treason. Thomas's brother, Henry, earl of Lancaster, 1281?-1345, was chief adviser to the young Edward III in getting rid of the dominance of the queen mother, Isabella, and her paramour, Roger de Mortimer, 1st earl of March. His son, Henry, duke of Lancaster, 1299?-1361, was made duke in 1351 for his excellent service as a military commander in the early part of the Hundred Years War. When he died without male heirs, his daughter Blanche married the fourth son of Edward III, John of Gaunt , who inherited the Lancaster lands in her right, and was made duke of Lancaster in 1362. His son Henry deposed (1399) Richard II and ascended the throne as Henry IV . In order to appear legitimate, Henry devised the fiction that his ancestor Edmund Crouchback had actually been Henry III's elder son but had been disinherited because he was a hunchback. Later Lancastrian kings were Henry V and Henry VI . The latter was deposed by the house of York in the course of the long dynastic struggle known as the Wars of the Roses . However, through the Beauforts, the legitimated descendants of John of Gaunt and Catherine Swynford (Rouet), the Lancastrian claims passed to the house of Tudor .