Earl of Leicester in the context of "Thomas, 2nd Earl of Lancaster"

The House of Lancaster was a cadet branch of the royal House of Plantagenet. The first house was created when King Henry III of England created the Earldom of Lancaster—from which the house was named—for his second son Edmund Crouchback in 1267. Edmund had already been created Earl of Leicester in 1265 and was granted the lands and privileges of Simon de Montfort, 6th Earl of Leicester, after de Montfort's death and attainder at the end of the Second Barons' War. When Edmund's son Thomas, 2nd Earl of Lancaster, inherited his father-in-law's estates and title of Earl of Lincoln he became at a stroke the most powerful nobleman in England, with lands throughout the kingdom and the ability to raise vast private armies to wield power at national and local levels. This brought him—and Henry, his younger brother—into conflict with their cousin King Edward II, leading to Thomas's execution. Henry inherited Thomas's titles and he and his son, who was also called Henry, gave loyal service to Edward's son King Edward III.

The second house of Lancaster was descended from John of Gaunt, a Plantagenet prince, who married the heiress of the first house, Blanche of Lancaster. Edward III married all his sons to wealthy English heiresses rather than following his predecessors' practice of finding continental political marriages for royal princes. Henry of Grosmont, 1st Duke of Lancaster, had no male heir so Edward married his son John to Henry's heiress daughter and John's third cousin Blanche of Lancaster. This gave John the vast wealth of the House of Lancaster. Their son Henry usurped the throne in 1399, creating one of the factions in the Wars of the Roses. There was an intermittent dynastic struggle between the descendants of Edward III. In these wars, the term "Lancastrian" became a reference to members of the family and their supporters. The family provided England with three kings: Henry IV (r. 1399–1413), Henry V (r. 1413–1422), and Henry VI (r. 1422–1461 and 1470–1471).

Edmund Crouchback (16 January 1245 – 5 June 1296) was a member of the royal Plantagenet Dynasty and the founder of the House of Lancaster. He was Earl of Leicester (1265–1296), Lancaster (1267–1296) and Derby (1269–1296) in England and Count Palatine of Champagne (1276–1284) in France.

Named after the 9th-century saint, Edmund was the second surviving son of King Henry III of England and Eleanor of Provence and the younger brother of King Edward I of England, to whom he was loyal as a diplomat and warrior. In 1254, the 9-year-old Edmund became involved in the "Sicilian business", in which his father accepted a papal offer granting the Kingdom of Sicily to Edmund, who made preparations to become king. However, Henry III could not provide funds for the operation, prompting the Papacy to withdraw the grant and give it to Edmund's uncle, Charles I of Anjou. The "Sicilian business" outraged the barons led by the Earl of Leicester and Edmund's uncle, Simon de Montfort, 6th Earl of Leicester, and was cited as one of the reasons for limiting Henry's power. Deterioration of relations between the barons and the king resulted in the Second Barons' War, in which the royal government, supported by Edmund, triumphed over the baronage following the death of Montfort in the Battle of Evesham in 1265.

Robert Dudley, 1st Earl of Leicester (24 June 1532 – 4 September 1588) was an English statesman and the favourite of Elizabeth I from her accession until his death. He was a suitor for the queen's hand for many years.

Dudley's youth was overshadowed by the downfall of his family in 1553 after his father, the Duke of Northumberland, had failed to prevent the accession of Mary I. Robert Dudley was condemned to death but was released in 1554 and took part in the Battle of St. Quentin under Mary's husband and co-ruler, Philip, which led to his full rehabilitation, but also to the death of his younger brother Henry. On Elizabeth I's accession in November 1558, Dudley was appointed Master of the Horse. In October 1562, he became a privy councillor and, in 1587, was appointed Lord Steward of the Royal Household. In 1564, Dudley became Earl of Leicester and, from 1563, one of the greatest landowners in North Wales and the English West Midlands by royal grants.

Simon de Montfort, 5th Earl of Leicester (c. 1175 – 25 June 1218), known as Simon IV (or V) de Montfort and as Simon de Montfort the Elder, was a French nobleman and knight of the early 13th century. He is widely regarded as one of the great military commanders of the Middle Ages. He took part in the Fourth Crusade and was one of the prominent figures of the Albigensian Crusade. Montfort is mostly noted for his campaigns in the latter, notably for his battle at Muret. He died at the Siege of Toulouse in 1218. He was Lord of Montfort from 1188 to his death and Earl of Leicester in England from 1204. He was also Viscount of Albi, Béziers and Carcassonne from 1213, as well as Count of Toulouse from 1215.

Thomas, 2nd Earl of Lancaster (c. 1278 – 22 March 1322) was an English nobleman of the first House of Lancaster, a cadet branch of the royal Plantagenet dynasty. He held the titles of Earl of Lancaster, Leicester, and Derby from 1296 until his death in 1322, and also those of Earl of Lincoln and Salisbury jure uxoris from 1311 to 1322. As one of the most powerful barons in England, Thomas became a leading figure in the baronial opposition to his first cousin, King Edward II.

The title of Earl of Lancaster was created in the Peerage of England in 1267. It was succeeded by the title Duke of Lancaster in 1351, which expired in 1361. (The most recent creation of the ducal title merged with the Crown in 1413.)

King Henry III of England created the Earldom of Lancaster—from which the royal house of Henry IV was named—for his second son, Edmund Crouchback, in 1267. Edmund had already been created Earl of Leicester in 1265 and following the Second Barons' War and the death and attainder of the king's rebellious brother-in-law Simon de Montfort, 6th Earl of Leicester in 1265, the latter's lands, including most notably Kenilworth Castle in Warwickshire, had been awarded to him.