However, the rise in power and influence of several gentry families and other political players, in the years leading up to Thomas' accession to the earldom, threatened the traditional dominance of the earls of Devon in the area.

Much of his life was spent in armed territorial struggle against his near-neighbour, Sir William Bonville of Shute, at a time when central control over the provinces was weak.

When the Wars of the Roses broke out, he was in the party of the queen, Margaret of Anjou, and was one of the Lancastrian commanders at the First Battle of St Albans, where he was wounded.

The Wars of the Roses later led to the deaths and executions of all three of Courtenay's sons, Thomas, Henry and John, and to the eventual attainder of his titles and forfeiture of his lands.

Based on his family's history and standing and on his own position as the leading landowner of the county, probably expected to take his place as the leader of Devon society.

Two men wearing Courtenay livery attacked Sir Philip Chetwynd, a friend of Bonville, on the road to London, apparent evidence that the council's arbitration of November 1440 had failed.

While Bonville was abroad, the King released Devon from his debts, including the recognisance for good behaviour, probably remitted by the influence of father-in-law, John Beaufort, Earl of Somerset.

[16][17] His advantageous marriage to Margaret Beaufort brought him links to the "court party", and Courtenay began to be selected by the king to serve on Westcountry commissions and was granted an annuity of £100 for his services.

[21] This promotion of his enemy Bonville may have prompted Devon to oppose the 'Court party' and to serve with his friend Richard Plantagenet, 3rd Duke of York during Jack Cade's Rebellion.

Having rescued the Duke of Somerset from an angry London mob, York himself had to flee, taking refuge on the Earl of Devon's barge rowing down the Thames.

The arrival of York (whether to suppress or aid the disturbances is uncertain) caused the two sides to make peace which, unsurprisingly, had no real meaning.

[22] York then embarked on his abortive attempt to take control of the royal government by force, his only allies being Courtenay and his sometime-associate, Edward Brooke, 6th Baron Cobham.

King Henry VI's madness and York's appointment as Protector in 1453/4 resulted in a partial rally in Courtenay's fortunes, including his re-appointment to commissions of the peace in the south-western counties, the key barometer of the local balance of power.

[30] Perhaps inspired by the way the Nevilles and York had forcefully ended their respective feuds with the Percies and the Duke of Somerset in the battle, Courtenay returned to Devon and commenced a further campaign of violence against Bonville and his allies, who were now attached to Warwick's party.

The violence began in October 1455 with the horrific murder by Courtenay allies of Nicholas Radford, an eminent Westcountry lawyer,[31] Recorder of Exeter and one of Bonville's councillors.

Several contemporary accounts, including the Paston Letters, record this event with the ensuing mock-funeral and coronary inquest accompanied by the singing of highly inappropriate songs, in tones of shock and horror unusual during the blunted sensitivities of the fifteenth century.

Early in December 1455, the King had dismissed Devon from the Commission of Peace, and citizens of Exeter had been instructed not to help his army of "misrule" in any way.

Originally, the government planned to bring him to trial for treason but this was abandoned once King Henry VI returned to sanity in February 1456, and York was removed as Protector.

Courtenay was also returned to the commission of the peace for Devonshire, seemingly the work of Queen Margaret of Anjou who had taken personal control of the court.

His rivals, Philip Courtenay and Lord Fitzwarin, were prevented from exercising commissions as Justices of the Peace, and were forced to leave the city.

Butler, Bonville's patron, and Sir John Fortescue, Chief Justice, arrived with a large entourage to investigate under a commission of oyer et terminer.

[4] At some time after 1421, Thomas de Courtenay married Lady Margaret Beaufort, daughter of John Beaufort, 1st Earl of Somerset (the first of the four illegitimate children of John of Gaunt (son of King Edward III of England) by his mistress, Katherine Swynford, later his wife) by his wife, Lady Margaret Holland.

However, modern authorities[46] have suggested, on the basis of the monument's heraldry, the effigy to be Margaret Beaufort (c. 1409 – 1449), the wife of Thomas de Courtenay, 5th Earl of Devon (1414–1458).