John I of Alençon, called the Sage (1385, Château d'Essay, – 25 October 1415, Azincourt), was the son of Peter II of Alençon and Marie de Chamaillard. In 1404, he succeeded his father as Count of Alençon and Perche. He was made Duke of Alençon in 1414.
He commanded the second division of the French army at the Battle of Agincourt. When the English broke through the first division, he led a countercharge. He is sometimes credited with killing Edward, Duke of York, wounding Humphrey, Duke of Gloucester, and cutting an ornament from the crown of Henry V of England; but he was then overpowered by King's bodyguard, and slain by the Welsh nobleman Dafydd Gam before he could yield himself.
In 1396, he married Marie of Brittany (1391–1446), daughter of John V, Duke of Brittany. They had five children:
He also had two illegitimate children:
| New creation | Duke of Alençon 1414–1415 |
Succeeded by John II |
| Preceded by Peter II |
Count of Alençon 1404–1414 |
Succeeded by John II |
| Count of Perche 1404–1415 |