John Grey, 1st Earl of Tankerville jure uxoris 6th Lord of Powys (after 1384 – 22 March 1421), KG, was an English peer who served with distinction in the Hundred Years' War between England and France under King Henry V. John Grey was the second son of Sir Thomas Grey (1359– 26 November 1400), of Berwick and Chillingham Castle, by his wife Joan Mowbray (d. 1410), a daughter of John de Mowbray, 4th Baron Mowbray by Elizabeth de Segrave.

Henry V granted the castle and seigneurie of Tilly in Normandy in November 1417, recently forfeited by Sir William Harcourt,[9] a supporter of the King's enemies.

[11] Grey was subsequently sent with a guard to Powys to bring the recently captured Lollard leader, Sir John Oldcastle, before Parliament.

[8] On 22 March 1420/1, while fording a river near the Chateau de Beaufort at the Battle of Baugé, Grey, Thomas of Lancaster, 1st Duke of Clarence, and many other of the English nobility were slain by a Franco-Scottish force, having incautiously engaged the enemy without proper preparation and with no archers in support.

[14] Joan de Cherleton survived her husband and in her widowhood in 1425 became heiress to her step-brother, Edmund Mortimer, 5th Earl of March,[9] who had earlier been the focus of the Southampton Plot.