Iorwerth mab Owain Gwynedd, known as Iorwerth Drwyndwn ('the flat-nosed';^[1] c. 1130 – 1174), was the eldest legitimate son of Owain Gwynedd (the king of Gwynedd) and his first wife Gwladus ferch Llywarch. He married Marared ferch Madog. His son Llywelyn ab Iorwerth^[1] eventually united the realm and became known as Llywelyn Fawr ('the Great'); he is one of Wales's most famous monarchs. Iorwerth received Nant Conwy as his inheritance from his father, Owain Gwynedd.^[1] However, he did not receive the crown succession, as was the normal tradition, because of his nose defect.^[1]

J. E. Lloyd states that Iorwerth was killed in battle at Pennant Melangell, in Powys, in 1174 during the wars deciding the succession following the death of his father.^[2][3]