Thomas of Lancaster (1388–1421), duke of Clarence , lieutenant of Ireland, and seneschal of England, was second son of Henry IV, and was appointed lieutenant of Ireland in July 1401 to secure a Lancastrian presence in the lordship. He arrived in Ireland in November 1401; but because he was still only 13, most of the task of governing fell to his deputy Stephen Scrope (qv), who was able to use the limited troops at his command to secure submissions from Gaelic lords. However, the peace gained by these military victories was imperilled by the chronically poor financial situation.
Lancaster had been promised an extremely large salary in his indentures, but this salary was perpetually in arrears. By August 1402 the Irish council wrote to the king that his son was penniless, having sold all his jewels and plate to pay for his administration. Lancaster remained in Ireland till November 1403 before leaving for England. He remained lieutenant, with Scrope, James Butler (qv), 3rd earl of Ormond, and Gerald fitz Maurice FitzGerald (qv), 5th earl of Kildare, serving as his deputies, but did not return to Ireland till August 1408. While in England he served with his brother, the future Henry V, in Wales and was also appointed admiral of England.
Lancaster's patents of office for Ireland were renegotiated twice (March 1406, March 1408), each time reducing the salary to be paid, but he still continued to draw his salary. He was eventually forced to return to Ireland, landing at Carlingford on 2 August 1408. One of his first actions was to arrest Kildare for treason, although nothing came of this. He campaigned in Leinster and was wounded in a battle at Kilmainham in the winter of 1408–9. Lancaster went to England on hearing rumours of his father's illness in March 1409, and never returned to Ireland. As Scrope had died in September 1408, Lancaster left Thomas Butler (qv), prior of Kilmainham, as his deputy. In 1409 he refused a proposal by his brother Henry that would compensate him for the lieutenancy but allow John Stanley to be appointed in his place. The prince of Wales felt that if Lancaster was drawing the salary of lieutenant of Ireland then he should actually go to Ireland, but the king did not support him in this.
Lancaster was created earl of Aumale and duke of Clarence on 9 July 1412 and given command of an expeditionary force sent to France to aid the duke of Orléans. By the time he reached France the disputes between Orléans and Burgundy had ended, so Clarence marched his force through France to Aquitaine. He presided over the trial of his cousin Richard, earl of Cambridge, in 1415. Although Clarence continued to favour an alliance with Orléans, he was an active participant in Henry V's campaigns in Normandy. He directed the siege of Rouen and was with his brother for the signing of the treaty of Troyes and Henry V's entry into Paris in December 1420. Clarence was killed facing a mixed force of Scots and French at Baugé on 22 March 1421, but his body was recovered and buried near his father in Canterbury cathedral.