From "A New History of Ireland", v IX, p 174:
1st Lord of Leinster by right of his wife, 1171-76.

From Irish Roots, 1994 #4, page 15, 'Surnames of County Leitrim':
One of the most momentous events in Irish history, the elopement of Dervorgilla, took place on O'Rourke territory. sometime around 1160 Tiernan O'Rourke's wife, Dervorgilla, eloped with Diarmuid MacMurrough. In 1166 O'Rourke marched on Leinster, where Diarmuid was king. MacMurrough sought aid from King Henry II of England and he, with the blessings of an English Pope, Adrian IV, sent Strongbow. This led effectively to the English occupation of Ireland.

From the book "The Oxford History of Ireland" edited by R. F. Foster, 1992, ISBN 0-19-285271-X, page 48:
King Dermot MacMurrough, [Richard's future father-in-law] initially recruited Richard fitzGilbert de Clare, earl of Pembroke, and a group of Cambro-Norman barons including the half-brothers Maurice FitzGerald and Robert FitzStephen, both sons of the Welsh princess Nesta [to help him regain his kingdom]. These latter were promised Wexford and two adjoining cantreds for their services, while de Clare, better known as 'Strongbow', was offered Dermot's daughter, Aoife in marriage and promised the whole province of Leinster on Dermot's death. Between 1169-1171 the Cambro-Normans not only reconquered all Leinster including Dublin for Dermot, but invaded the neighboring province of Meath and harried Tighearnán O'Rourke's kingdom of Bréifne.

One family, through a combination of intrigue and diplomacy, rose to become the wealthiest family in thirteenth century England, and later members of the dynasty were to influence the country's future by marrying into the Plantagenet royal family.
The family in question is that of the de Clares. Originally a Norman family, they took their name from Clare in Suffolk where their first castle, and the seat of their barony, was situated. By the thirteenth century, the family held vast estates in Wales, Ireland, and twenty two English counties.

The first recorded member of the de Clare dynasty was Godfrey, Count of Eu. Godfrey was an illegitimate son of Richard of Normandy, and his son Gilbert was assassinated in 1040. Gilbert's sons accompanied William in his invasion of England in the late eleventh century. They were suitably rewarded for their support - Baldwin de Clare became Sheriff of Devonshire, and his brother Richard de Clare was given control of 170 estates in Suffolk (95 of which were attached to Clare Castle. Although Baldwin did not marry, Richard's marriage to Rohais Giffard produced three sons (Richard, Roger and Gilbert) and two daughters (Rohais and one unknown). Richard and Rohais de Clare also set about building a priory at St Neots (now in Cambridgeshire), which was finished around 1100; Richard never saw the dedication service however, as he died around 1090.

Richard and Rohais' children managed to involve themselves in a great deal of intrigue. Roger and Gilbert were present at the murder of William II in 1100, and the unknown daughter was married to Walter Tyrol, who was William's murderer. Gilbert had also been involved in rebellion in 1088 and 1095, so it would seem that the de Clare family were keen to establish a leading role in British politics from an early stage. The third of Richard's sons, named Richard after his father, seemed more content with his lot, as he is not believed to have been involved in any such high level intrigue as his siblings; saying this however, his son Gilbert kept up family tradition through being one of the twenty five barons involved in the administration of the Magna Carta in 1215. The younger Richard also married Amicia, daughter of the Earl of Gloucester, inheriting the title and passing it down through an unknown son after his death in 1217.

Five sons and one daughter were born to the Gilbert de Clare present at William IIs death; his son Gilbert became the powerful Earl of Pembroke, holding and expanding lands in Wales and Ireland; Pembroke's son Richard earned the battle name "Strongbow", presumably for carrying on his families traditional prowess in battle.
Pembroke's son Richard first earned his reputation as a warrior by taking a force of warriors to Ireland, where he stormed the Norse-Irish city of Dublin; his progress in conquest was so successful that Henry I feared that Richard had grown too powerful and ordered him to return to his lands in Wales... Richard stubbornly refused and fought on. Eventually, his allies submitted to Henry's demand and Richard had to follow suit, however, after reaffirming his allegiance to Henry, a large force returned to Ireland and Richard held control over the lands of Leinster. He also found time between conquering Ireland to father two children, Isabel and Robert; Isabel married William Marshall and their daughter Isabella wed the younger Gilbert de Clare, Earl of Gloucester. This reunited the two branches of the de Clare family early in the thirteenth century.

Richard Strongbow went as an adventurer (1170) to Ireland at the request of the hard-pressed Dermot McMurrough, king of Leinster. Strongbow subdued much of East Ireland, including Dublin, in victories over Rory O’Connor, king of Connacht, and married Dermot’s daughter. Henry II of England, although he had given permission for the earl’s expedition, visited him in 1171 to claim the rich coastal cities and to receive Strongbow’s homage for the fief of the interior of Leinster. Pembroke fought for Henry in Normandy and was rewarded by a grant of additional territory in Ireland. He then returned to Ireland as the king’s governor. Badly defeated (1174) at Thurles, he was engaged in almost continuous fighting against the Irish until his death.

Gerald of Wales describes Strongbow as a tall man with red hair, freckles, grey eyes and a soft (weak) voice. "In war Strongbow was more of a leader than a soldier. . . . When he took-up his position in the midst of battle, he stood firm as an immovable standard around which his men could re-group and take refuge. In war he remained steadfast and reliable in good fortune and bad alike. . . ." If a man who was Strongbow's contemporary and not overly fond of him could describe him thus, Strongbow must have been a unique man. Strongbow had the patience and intelligence to not openly defy King Henry II, despite being denied what he must have seen as his rightful inheritance. He had the military skills and abilities of a commander that enabled him to conquer great lands in Ireland and the sagacity of a diplomat that allowed him to offer those conquests to his king and vassal lord, Henry II.