Richard, the son of Roger of Clare 2nd Earl of Hertford, was more commonly known as the Earl of Clare.

He married Amicie Fitzwilliam, 4th Countess of Gloucester (1160-1220), second daughter and co-heiress of William Fitz Robert. In 1183 he obtained, through marriage, control of Glamorgan. He was present at the coronations of King Richard I at Westminster on 3 September 1189, and King John on 27 May 1199. He was also present at the homage of King William of Scotland as English Earl of Huntingdon at Lincoln.

In 1200, King John became involved in a long-drawn out and expensive war with France and he was forced to introduce new taxes to pay for his army which created a great deal of resentment in England. His position was not helped when, in 1205, the king's army lost control of Normandy, Brittany, Anjou and Maine. Gradually the Norman barons began to conspire against King John in 1209 and 1212; promises made to the northern barons and John's submission to universal rule of the papacy in 1213 delayed a French invasion.

Over the course of his reign a combination of higher taxes, unsuccessful wars that resulted in the loss of English barons' titled possessions in Normandy following the Battle of Bouvines (1214), and the conflict with Pope Innocent III (ending with John's submission in 1213) had made King John unpopular with many of his barons. By 1215, King John made another desperate attempt to gain control of his lost territory in France. Once again he was defeated and was forced to pay £40,000 to obtain a truce.

When he tried to obtain this money by imposing yet another tax, the barons rebelled with Richard de Clare recognised as one of the leaders. Few barons remained loyal, and in most areas of the country, King John had very little support. What was unusual about the 1215 rebellion was that the rebels had no obvious replacement for John. Instead of a claimant to the throne, the barons decided to base their rebellion around John's oppressive government. In January 1215, the barons made an oath that they would "stand fast for the liberty of the church and the realm", and they demanded that King John confirm the Charter of Liberties, from what they viewed as a golden age.

John attempted to use the lengthy negotiations to avoid a confrontation while he waited for support from the Pope and hired mercenaries, adopting various measures to weaken the rebels' position and improve his own, including taking the cross as a crusader in March 1215 (which the Pope applauded but most other observers considered insincere), demanding a new oath of allegiance, and confirming London's city charter in May 1215. During negotiations between January and June 1215, a document was produced, The Unknown Charter of Liberties'. In May, King John offered to submit issues to a committee of arbitration with Pope Innocent III as the supreme arbiter, but the barons continued in their defiance.

With the support of Prince Louis the French Heir and of King Alexander II of the Scots, they entered London in force on 10 June 1215, with the city showing its sympathy with their cause by opening its gates to them. They, and many of the moderates not in overt rebellion, forced King John to agree to a document later known as the 'Articles of the Barons', to which his Great Seal was attached in the meadow at Runnymede on 15 June 1215.

In return, the barons renewed their oaths to King John on 19 June 1215, which is when the document Magna Carta was created. The Magna Carta, resulted in no new taxes without the support of his barons, a reduction in the power of his sheriffs and the right of a fair trial for all freemen. Magna Carta was the first document forced onto a King of England by a group of his subjects, the feudal barons, in an attempt to limit his powers by law and protect their privileges. The charter was an important part of the extensive historical process that led to the rule of constitutional law in the English speaking world.

The barons had doubts whether King John, sinfully lustful and lacking in piety, could be trusted to keep his word and a small group were given the task of ensuring he upheld the Magna Carta. Two of the 25 barons chosen as surety for its enforcement were Richard de Clare and his son Gilbert. Neither John nor the rebel barons seriously attempted to implement the peace accord. The rebel barons suspected that the proposed baronial council would be unacceptable to John and that he would challenge the legality of the charter; they packed the baronial council with their own hardliners and refused to demobilise their forces or surrender London as agreed.

Despite his promises to the contrary, John appealed to Innocent for help, observing that the charter compromised the pope's rights under the 1213 agreement that had appointed him John's feudal lord. Innocent obliged; he declared the charter "not only shameful and demeaning, but illegal and unjust" and excommunicated the rebel barons. The failure of the agreement led rapidly to the First Barons' War and subsequently John’s own illness and early death, but not before he turned his wrath on Richard of Clare, who in November 1215 saw his lands in counties Cambridge, Norfolk, Suffolk and Essex revoked and granted to Robert de Betun.

Richard’s son, Gilbert de Clare, 4th Earl of Hertford, 5th Earl of Gloucester (1180 – 25 October 1230) inherited the remaining Clare estates on the death of his father in 1217. He also inherited from his mother, Amice Fitz William, the estates of Gloucester and the honour of St Hilary. On becoming one of the Magna Carta sureties he championed King Louis "le Dauphin" of France in the First Barons' War as a replacement to King John, fighting at Lincoln under the baronial banner.

He was taken prisoner in 1217 by William Marshal, whose daughter Isabel he later married on 9 October. In 1223 he accompanied his brother-in-law, Earl Marshal, in an expedition into Wales. In 1225 he was present at the confirmation of the Magna Carta by Henry III and in 1228 he led an army against the Welsh, capturing Morgan Gam, the grandson of the leader or the Welsh rebellion Ifor Bach, lord of Senghenydd. Gilbert de Clare then joined in an expedition to Brittany, but died on his way back to Penrose. His body was conveyed home by way of Plymouth and Cranborne to Tewkesbury.

He was succeeded by Richard de Clare, 5th Earl of Hertford, 6th Earl of Gloucester (4 August 1222 – 14 July 1262) who fortified several of the Glamorgan castles against the Welsh uprisings. One of which was Llantrisant in 1246, where he made a home for his family. At Llantrisant in 1252 Richard and his wife, Maud de Lacy, (daughter of John de Lacy, 1st Earl of Lincoln) had a daughter called Margaret at the Castle. On 6 October 1272, Margaret, married Edmund, the 2nd Earl of Cornwall at a chapel in Ruislip. Edmund was knighted a few days later by Henry III at Westminster Abbey. During Richard De Clare’s tenure at the Castle, Llantrisant was fiercely raided by the supporters of Llywelyn ap Gruffydd or Llywelyn Ein Llyw Olaf ("Llywelyn, Our Last Leader") (c. 1223 – 11 December 1282), the last prince of an independent Wales before its conquest by Edward I.

Llantrisant Castle remained in Norman hands by the time Richard de Clare’s eldest son and successor came to power. He was Gilbert de Clare, 6th Earl of Hertford, 7th Earl of Gloucester (2 September 1243 – 7 December 1295), one of the most powerful and brutal of all nobles. He was known as "Red" Gilbert de Clare or "the red earl", probably because of his hair colour or fiery temper in battle. Born in Christchurch, Hampshire, he inherited his father's estates in 1262, taking on the titles, including Lord of Glamorgan, from 1263. His wife was Joan of Acre (April 1272 – 23 April 1307) an English princess, and daughter of Edward I and Queen Eleanor of Castile. It was one of their daughters, Elizabeth de Clare (16 September 1295 – 4 November 1360) who founded Clare College, Cambridge.

In April 1264, Gilbert de Clare led the massacre of the Jews at Canterbury as Simon de Montfort had done in Leicester. Gilbert’s castles of Kingston and Tonbridge were taken by Henry III. On 12 May de Clare and de Montfort were denounced as traitors. Two days later, just before the Battle of Lewes, on 14 May, Simon de Montfort knighted the Earl and his brother Thomas. De Clare commanded the central division of the Baronial army, which formed up on the Downs west of Lewes. When Prince Edward had left the field in pursuit of Montfort's routed left wing, the King and Earl of Cornwall were thrown back to the town. Henry took refuge in the Priory of St Pancras, and Gilbert accepted the surrender of the Earl of Cornwall, who had hidden in a windmill. Montfort and De Clare were now supreme and de Montfort in effect de facto King of England.

On 20 October 1264, De Clare and his associates were excommunicated by Pope Clement IV. In the following month, by which time they had obtained possession of Gloucester and Bristol, he was proclaimed to be a rebel. However at this point he changed sides as he fell out with de Montfort and De Clare, in order to prevent de Montfort's escape, destroyed ships at the port of Bristol and the bridge over the River Severn at Gloucester. Having changed sides, De Clare shared the Prince's victory at Kenilworth on 16 July, and in the Battle of Evesham, 4 August, in which de Montfort was slain. Gilbert de Clare commanded the second division and contributed largely to the victory. On 24 June 1268 he took the Cross at Northampton in repentance and contrition for his past misdeeds.

In October 1265, as a reward for supporting Prince Edward, Gilbert was given the castle and title of Abergavenny and honour and castle of Brecknock. At Michaelmas his disputes with Prince Llewellyn of Wales were submitted to arbitration, but without a final settlement. Meanwhile he began building Caerphilly Castle into a fortress. At the end of 1268 he refused to obey the King's summons to attend parliament, alleging that, owing to the constant inroads of Llewelyn, his Welsh estates, including Llantrisant and Caerphilly Castles, needed his presence for their defence. At the death of Henry III, on 16 November 1272, De Clare took the lead in swearing loyalty to Edward I, who was then in Sicily on his return from the Crusade. The next day, with the Archbishop of York, he entered London and proclaimed peace to all, Christians and Jews, and for the first time, secured the acknowledgment of the right of the King's eldest son to succeed to the throne immediately.

Afterwards he was joint Guardian of England, during the King's absence, and on the new King's arrival in England, in August 1274, entertained him at Tonbridge Castle. During Edward's invasion of Wales in 1282, De Clare insisted on leading an attack into the south. King Edward made De Clare the commander of the southern army. However, it faced disaster after being heavily defeated at the Battle of Llandeilo Fawr. De Clare was relieved of his position as the southern commander and was replaced by William de Valence, 1st Earl of Pembroke.

In 1291, Gilbert quarrelled with the Earl of Hereford, Humphrey de Bohun, about the Lordship of Brecknock, where de Bohun accused de Clare of building a castle on his land which culminated in a private war between them. Although it was a given right for Marcher Lords to wage private war the King tested this right in this case, first calling them before a court of their Marcher peers, then realising the outcome would be coloured by their likely avoidance of prejudicing one of their greatest rights they were both called before the superior court, the Kings own. At this both were imprisoned by the King, both sentenced to having their lands forfeit for life and De Clare, as the aggressor, was fined 10,000 marks, and the Earl of Hereford 1,000 marks. They were released almost immediately and both of their lands completely restored to them - however they had both been taught a public lesson and their prestige began to diminish.

A year before De Clare’s death, his castle in Llantrisant was damaged once more. This time it was an uprising against the Norman overlords by Madog ap Llywelyn which began in 1294. Known as Prince Madoc, he was from the House of Aberffraw and a distant relation of Llywelyn ap Gruffudd. In the autumn of 1294, Madog put himself at the head of a national revolt in response to the actions of new royal administrators in north and west Wales and the imposition of taxes such as that levied on one fifteenth of all moveables. As a royal prince and the fifth cousin of the last Prince of Aberffraw (Dafydd ap Gruffudd, the executed brother of Llywelyn), Madog declared himself to be the lawful successor and assumed the royal titles of his predecessors including "Prince of Wales". The uprising quickly spread to south Wales led by Cynan ap Maredudd, Maelgwn ap Rhys, and Morgan ap Maredudd of Gwynllwg in Glamorgan.

Caernarfon was overrun by Madog's forces and the castle occupied, as were the castles at Hawarden, Ruthin, and Denbigh. Criccieth Castle was besieged by Madog's forces for several months, as was Harlech Morlais castle was captured under the aegis of Morgan in the south, and Cynan ap Maredudd besieged the castle at Builth for a period of six weeks. Half the town of Caerphilly was burnt - although the castle itself held out - and, further south, Kenfig and Llantrisant castles was sacked. In north Wales, attempts were made by many English landowners to retrieve the situation. The lord of Denbigh, Henry de Lacy led a march to Denbigh after the castle there was beiseged; however, he was ambushed outside the town on 11 November, and in the ensuing battle his force was routed by the rebels. In north-east Wales, Reginald de Grey was more successful, stationing substantial garrisons at Flint and Rhuddlan - neither castle fell to the rebels, though Flint was subjected to a lengthy siege. Many other castles across Wales were besieged and several towns burnt.

In December 1294 Edward I led an army into north Wales to quell the revolt, stopping at Wrexham, Denbigh, Abergele, and elsewhere on his way to Conwy Castle, which he reached shortly before Christmas. His campaign was timely, for several castles remained in serious danger - Harlech Castle was defended at one point by just 37 men and Edwand himself was besieged at Conwy Castle until he was relieved by his navy in 1295. A final battle between Madog's men and those of the English crown occurred at the battle of Maes Moydog in Powys in 1295. The Welsh army were defeated tactically when they were ambushed by the Earl of Warwick.

The Welsh regained their composure and attempted to destroy the English cavalry by using the "porcupine" pike men formation, or schiltron, a formation favoured by the Scots armies against English knights. In the process they were showered with arrows from English archers and suffered very heavy losses. Madog barely escaped with his life and was a fugitive until his unconditional surrender to John de Havering in Snowdonia in late July or early August 1295. He was subsequently taken to London and all that is known of his fate is that he did not suffer the supreme penalty; he was still alive in 1312 and was survived by his sons. The revolt of 1294-95 elicited a harsh response from Edward I in the form of humiliating and punitive ordinances further restricting the civil rights and economic and social opportunities of the Welsh.