English royal house, branch of the
Plantagenets. It originated 1267 when Edmund
(died 1296), the younger son of Henry III,
was granted the earldom of Lancaster.
Converted to a duchy for Henry of Grosmont
(died 1361), it passed to John of Gaunt 1362
by his marriage to Blanche, Henry's daughter.
John's son, Henry IV, established the royal
dynasty of Lancaster 1399, and he was
followed by two more Lancastrian kings, Henry
V and Henry VI.