Thomas Mowbray Norfolk, 1st duke of 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