Maredudd ap Rhys Grug (died 1271), was the son of Rhys Gryg (a Welsh prince of Deheubarth) and Mathilde de Clare (a daughter of Richard de Clare, 3rd Earl of Hertford, Marcher Lord of Cardigan).
When his father died, in 1234, Maredudd was still young, and his wardship was entrusted to Gilbert Marshal, 4th Earl of Pembroke;[1] their mothers were distant cousins.
In 1241, Maredudd married Gilbert's niece, Isobella;[1] the marriage had probably been arranged earlier.
Maredudd contributed significantly in the 1257 battle of Cymerau where the Welsh side were victorious.
He was found guilty by a council of native lords and imprisoned in the castle at Criccieth.