The House of Lancaster was a cadet branch of the royal House of Plantagenet. The first house was created when King Henry III of England created the Earldom of Lancaster—from which the house was named—for his second son Edmund Crouchback in 1267. Edmund had already been created Earl of Leicester in 1265 and was granted the lands and privileges of Simon de Montfort, 6th Earl of Leicester, after de Montfort's death and attainder at the end of the Second Barons' War. When Edmund's son Thomas, 2nd Earl of Lancaster, inherited his father-in-law's estates and title of Earl of Lincoln he became at a stroke the most powerful nobleman in England, with lands throughout the kingdom and the ability to raise vast private armies to wield power at national and local levels. This brought him—and Henry, his younger brother—into conflict with their cousin King Edward II, leading to Thomas's execution. Henry inherited Thomas's titles and he and his son, who was also called Henry, gave loyal service to Edward's son King Edward III.

The House of Plantagenet was a royal house which originated in the French County of Anjou. The name Plantagenet is used by modern historians to identify four distinct royal houses: the Angevins, who were also counts of Anjou; the main line of the Plantagenets following the loss of Anjou; and the Houses of Lancaster and York, two of the Plantagenets cadet branches. The family held the English throne from 1154, with the accession of Henry II, until 1485, when Richard III died.