William IV, Duke of Aquitaine
| William IV | |
|---|---|
| Duke of Aquitaine and Count of Poitou | |
| Reign | 963–990 |
| Predecessor | William III, Duke of Aquitaine |
| Successor | William V, Duke of Aquitaine |
| Born | c. 937 Poitiers |
| Died | 3 February 994 |
| Burial | |
| Spouse | Emma of Blois |
| Issue | William V, Duke of Aquitaine Ebles |
| House | Ramnulfids |
| Father | William III, Duke of Aquitaine |
| Mother | Gerloc of Normandy |
William IV (c. 937 – 3 February 994), called Fierebras (meaning "Proud Arm", from the French Fier-à-bras (which means Proud-to-Arm), in turn from the Latin Ferox brachium) (which means A Fierce Arm), was the Duke of Aquitaine and Count of Poitou from 963 to his retirement in 990.