| Gilbert de Clare | |
| 4th Earl of Hertford 5th Earl of Gloucester 1st Lord of Glamorgan | |
| Succession: | Hereditary |
| More: | no |
| Reign: | 1217–1230 1225–1230 |
| Reign-Type: | Earl of Hertford Earl of Gloucester |
| Predecessor: | Richard de Clare, 3rd Earl of Hertford |
| Successor: | Richard de Clare, 6th Earl of Gloucester |
| Suc-Type: | Successor |
| Spouse: | Isabel Marshal |
| Spouse-Type: | Spouse |
| Noble Family: | de Clare |
| House-Type: | Nobility |
| Father: | Richard de Clare, 3rd Earl of Hertford |
| Mother: | Amice Fitz William, suo jure Countess of Gloucester |
| Birth Date: | 1180 |
| Birth Place: | Hertford, Hertfordshire, England |
| Death Date: | 25 October 1230 |
| Death Place: | Brittany, France |
| Burial Place: | Tonbridge Priory |
| Occupation: | Peerage of England |
Gilbert de Clare, 4th Earl of Hertford, 5th Earl of Gloucester, 1st Lord of Glamorgan, 7th Lord of Clare (1180 – 25 October 1230) was the son of Richard de Clare, 3rd Earl of Hertford (c. 1153–1217), from whom he inherited the Clare estates. He also inherited from his mother, Amice Fitz William, the estates of Gloucester and the honour of St. Hilary, and from Rohese, an ancestor, the moiety of the Giffard estates. In June 1202, he was entrusted with the lands of Harfleur and Montrevillers.[1]
In 1215, Gilbert and his father were two of the barons who made Magna Carta sureties and championed Louis "le Dauphin" of France in the First Barons' War, fighting at Lincoln under the baronial banner. He was taken prisoner in 1217 by William Marshal, whose daughter Isabel he later married on 9 October, her 17th birthday.
In 1223, he accompanied his brother-in-law, Earl Marshal, in an expedition into Wales. In 1225 he was present at the confirmation of Magna Carta by Henry III. In 1228, he led an army against the Welsh, capturing Morgan Gam, who was released the next year.
He then joined in an expedition to Brittany, but died on his way back to Penrose in that duchy. His body was conveyed home by way of Plymouth and Cranborne to Tewkesbury. His arms were: Or, three chevronels gules.
Gilbert de Clare had six children by his wife Isabel Marshal, great-grandmother of King Robert the Bruce:
His widow Isabel later married the King of the Romans & Earl of Cornwall, Richard Plantagenet, of the House of Plantagenet.