Norfolk, Thomas Mowbray, 1st duke of, c.1366–1399, English nobleman. He was created earl of Nottingham in 1383, and in 1385 he was made earl marshal of England for life. He joined Thomas of Woodstock, duke of Gloucester, and the other baronial opponents of Richard II in 1387 and was one of the five lords appellant who "appealed" (i.e., accused) the king's favorites of treason and secured their conviction in the Merciless Parliament of 1388. After Richard regained control in 1389, however, he was conciliatory to Nottingham, who accompanied him to Ireland in 1394. In 1397, Nottingham aided the king in bringing to trial his former associates, Gloucester and the earls of Arundel and Warwick. Gloucester was placed in his custody, and he was possibly responsible for his murder. Although created duke of Norfolk in 1397, he began to fear that the king might turn on him and confided in the other remaining lord appellant, the duke of Hereford (later Henry IV). A dispute arose between Norfolk and Hereford when Hereford told the king of Norfolk's suspicions, and trial by combat was proposed. At the last moment, however, Richard intervened and banished both from the country, Norfolk for life. He died in Italy. A version of the story is told in Shakespeare's Richard II.