Thomas of Lancaster, 1st Duke of Clarence, English soldier and politician, Lord High Steward of England (b. 1388)
Thomas of Lancaster, Duke of Clarence (autumn 1387 – 22 March 1421) was a medieval English prince and soldier, the second son of Henry IV of England, brother of Henry V, and heir to the throne in the event of his brother's death. He acted as councillor and aide to both.

After his father's death, he participated in his brother's military campaigns in France during the Hundred Years' War. Left in charge of English forces in France when Henry returned temporarily to England after his marriage to Catherine of Valois, Thomas led the English in their disastrous defeat at the hands of a mainly Scottish force that came to the aid of the French at the Battle of Baugé. In a rash attack, he and his leading knights were surrounded, and Thomas was killed.