ROS, or DE Ros, the name of a noble English family. Robert de Ros (d. 1227), a son of Everard de Ros (d. 1191) of Helmsley, or Hamlake, in Yorkshire, possessed lands in Yorkshire, including Ros, or Ross, in Holderness, and also in Normandy. He served King John in several ways, both in England and abroad, and obtained lands in Northumberland, where he built a castle at Wark, or Werke. About 1215, however, he deserted the king and became one of the leaders of the baronial party, being one of the twenty-five executors of Magna Carta and fighting against John when he repudiated this engagement. He submitted to Henry III. and became a monk before he died in 1227. His wife was Isabella, daughter of William the Lion, king of Scotland, by whom he had two sons, William and Robert. Robert de Ros the younger (d. 1274), was an itinerant justice under Henry III., but later he was one of the barons who fought against this king. He passed much of his time, however, in Scotland, where he held a barony and where he was one of the guardians of Margaret, the English bride of King Alexander III. His son Robert was summoned to parliament as Lord Ros de Werke in 1295; just afterwards he revolted against Edward I. and his lands were forfeited. William de Ros (d. 1258), the elder son of the executor of Magna Carta, had a son Robert (d. 1285), who was summoned to parliament as a baron by Simon de Montfort in 1264; he was also summoned to parliament by Edward I. His son William, 2nd baron Ros of Helmsley, or Hamlake (d. 1317), obtained Belvoir Castle in Leicestershire through his mother Isabel, daughter of William d'Albini. He was one of the minor claimants for the crown of Scotland in 1292, and soon afterwards he obtained the lands in Northumberland which had been taken from his traitorous cousin Robert de Ros. His second son, John de Ros (d. 1338), was a courtier under Edward II. Later he joined Edward's queen, Isabella, was summoned to parliament by Edward III., and distinguished himself on the sea. Another John de Ros (d. 1332), bishop of Carlisle from 1325 to 1332, was doubtless a member of this family.
The second baron's descendants retained the barony of Ros until the death of Edmund de Ros, the nth baron, in October 1508. Edmund's nephew Sir George Manners (d. 1513), of Belvoir and Helmsley, then claimed it, and was called Lord Ros, or Roos. His son, Thomas Manners, the 13th baron (d. 1543), was created earl of Rutland in 1525, but the barony was separated from the earldom when Thomas's grandson Edward died in 1387, leaving an only child, Elizabeth (d. 1591), who, as heir general of the family, became Baroness Ros, or Roos. Elizabeth married into the Cecil family, and when her only child, William Cecil, died in 1618, the barony reverted to the Manners family, Francis Manners, 6th earl of Rutland (1578-1632), becoming the 18th baron. On his death the barony again passed to a female, his daughter Katherine, through whom it came to the family of Villiers. Then in 1806, after a long abeyance, Charlotte (1769-1831), daughter of the Hon. Robert Boyle, and a descendant of the Manners family, was declared Baroness Ros, or Roos. She married Lord Henry Fitzgerald, and their son, Henry William Fitzgerald-de-Ros (1793-1839), became the 22nd baron on his mother's death. In 1907, on her father's death, Mary Frances, wife of the Hon. Anthony Dawson, became Baroness Ros, or rather, De Ros, which is the present form of the title. For a long time after they had ceased to hold the barony the earls and dukes of Rutland continued to style themselves Lords Roos.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)