The Mortimers were a powerful Marcher family that begin with Ranulf, who became lord of Wigmore after 1075. He was Norman, naturally, and was the Seigneur of St. Victor-en-Caux in Normandy. http://en.wikipedia.org/wiki/Ralf_de_Mortimer
Once in England, however, the family rose to power and as far as I can tell, did everything in their power to hold onto it, regardless of how many times they switched allegiances between the English crown, the Welsh crown, and outright rebellion.
“In historical terms we can go back to the Domesday Book for the first clear reference to Wigmore Castle. The relevant entry read “Ralph de Mortimer holds Wigmore Castle”, but he was not the nobleman to whom we can attribute the building of the stronghold. That honor goes to William Fitzosbern, but this Norman, one of the Conqueror’s captains, incurred William’s wrath in 1075 with an act of treachery and he was replaced as castellan by Mortimer.
Thus started the Mortimer association with Wigmore which was to last the best part of four centuries. Adopting the name of the Normandy castle and village of Mortemer en Brai, the House of Mortimer was to become one of the most powerful families in England. Indeed, at one time, early in the reign of Edward III, it’s head, Roger, was for a while the de facto ruler of the country.The Mortimers were archetypal Marcher Lords. The latter were a class of noblemen established by the Norman kings of England to police The Marches, which were their Welsh, and to a lesser degree, Scottish border. In return for this service the lords were allotted vast tracts of territory in these regions. More than that, though, they were afforded wide ranging powers not available in English-based counterparts – these in return for providing a defensive cushion between the rebellious Welsh and the shires adjacent to Wales.
For example, they were allowed to raise their own armies, exact taxes and build castles without the sovereign’s consent. Marcher Lords were acquisitive by nature and took every opportunity to enlarge upon their dominions. This process took the form of either taking possession by force or by engaging themselves or their offspring in marriages made profitable by handsome dowries of land and property.” http://www.castlewales.com/wigmore.html
Notable family members include:
Ranulph: “After William the Conqueror‘s death, the Kingdom of England and the Duchy of Normandy were divided. Ranulph of Mortemer joined the ranks of the Rebellion of 1088 against the new King of England, William Rufus. Together with Norman, English and Welsh Marcher Lords, they invaded and conquered the lands ofHereford, Gloucester and Worcestershire. A year later, the revolt failed and the marches of Normandy, from Maine to the Evrecin, were in disorder. King Rufus took advantage of this opportunity to align with the barons of Upper Normandy by bribing them. Of these barons, Ranulph maintained his land by accepting a bribe from the King in which he had to give his support to England. He did this by garrisoning his castle and sacking surrounding enemy territories as an attack against the new Duke of Normandy, Robert Curthose. The Norman baron allegiance set the stage for a race between the heirs of William I, where the Duke of Normandy and the King of England sought to gain as much support from powerful and influential houses as possible against each other.” http://en.wikipedia.org/wiki/Ralf_de_Mortimer
Hugh (before 1117 to 26 Feb 1180/1): Ardently supported King Stephen against Maud during the Anarchy.
Roger (1231 – 30 October 1282): This was the 1st Baron Mortimer and one of the most powerful lords of the 13th century. He was the child of Ralph, and his mother, Gwladys, daughter of Llywelyn the Great.
“By February 1254 Roger Mortimer succeeded in being assigned certain lands in Brecon Barony as part of the Braose settlement, although the Bohun’s successfully stalled from giving him anything. In November 1256 war again came to Wales when Prince Llywelyn ap Gruffydd and his brother Dafydd invaded the Marches of Wales and annexed them to the principality of Gwynedd. War generally favoured Prince Llywelyn in this period and in November to December 1262 he convincingly defeated Roger Mortimer and seized much of Radnorshire and Breconshire from the Marchers. On 3 March 1263 the Marchers counter-attacked and defeated the Princes of Deheubarth at the battle of Abergavenny. At this point the Lord Edward, later to be Edward I (1272-1307) and known as the Hammer of the Scots, arrived with an army from Gascony and transferred to Roger Mortimer the castles of Brecon, Huntington and Hay on Wye, which Mortimer claimed against the Bohuns.
Two months later Humphrey Bohun Junior, the disenfranchised lord of Brecon, was amongst those who raised the standard of rebellion against King Henry III and his son and heir, the Lord Edward. This was the beginning of the Barons’ War of 1263-66. In July 1264 the famous Earl Simon Montfort appeared before the walls of Hay on Wye Castle and forced its Mortimer garrison to surrender. Huntington Castle was probably also besieged, but did not surrender before Roger Mortimer himself was surrounded at Montgomery Castle and forced to surrender at the end of August. The Mortimer garrison in Huntington Castle remained true to their lord’s cause and despite the many defeats suffered by Mortimer. They kept the Baronial army from occupying the castle until, on 4 August 1265, Roger Mortimer commanded a third of the Marcher army, which under the Lord Edward, defeated and killed Earl Simon Montfort at the battle of Evesham. Another baronial casualty, who in fact survived to fight another day, was Lord John Balun of Much Marcle!
After Evesham Roger Mortimer took Hay on Wye Castle back and used this and Huntington Castle as a base for regaining Brecon Castle from Prince Llywelyn, who had taken the castle in May 1263. On 15 May 1266 Roger Mortimer’s army was all but annihilated just short of Brecon. This disaster was followed by another Civil War with Roger marching against the Earl of Gloucester who had seized London town for the barons. As the royal army approached a novel plan was put before the king. Burn London to the ground by sending small birds with burning twigs tied to the feet over the town walls! Thankfully more humane methods prevailed and a truce led to final peace which included Roger Mortimer returning Huntington and Hay on Wye Castles back to the Bohuns as part of a general peace settlement.” http://www.castlewales.com/hunting.html
Roger Mortimer (25 April 1287 – 29 November 1330): He was the grandson of the aforementioned Roger, through the second son, Edmund.
He sided with Lancaster in his opposition to the king, was taken prisoner in 1322, and condemned to perpetual captivity. Escaping in 1324 he fled to France. In 1325 Queen Isabella being sent over to the French court, Mortimer formed an intrigue with her, and in the next year accompanied her to England. The king fled, and was subsequently deposed, and in 1327 Mortimer was master of the situation.
For nearly four years the queen and Mortimer ruled the country. All attempts to upset or curtail their power were defeated; the Earl of Lancaster, who endeavoured to rival Mortimer, was compelled to submit in 1328, and a plot set on foot by the king’s uncle, Edmund, Earl of Kent, which had for its object the restoration ofEdward II, who was supposed to be still alive, failed utterly, and Kent was executed (1330).
But this was Mortimer’s last act, for the young king [Edward III] had determined to rid himself of the intolerable yoke he had borne so long. Mortimer was surprised in Nottingham Castle, arraigned as a traitor, accused of the death of Edward II and the Earl of Kent, and hanged, to the universal joy of the nation. His arrogance and vindictiveness recalled the worst features of the Despencers, and his adultery with the queen rendered him still more odious in the eyes of the people.”
That’s a lot of opinion there. You can read about his story in my friend N. Gemini Sasson’s books: Isabeau and The King Must Die