Madog ap Rhiryd was a 12th-century Welsh prince of part of Powys.
In 1110 he allied himself with his cousin, Owain ap Cadwgan, against Henry I of England.
After Henry stripped Owain of his title and replaced him with Iorwerth ap Bleddyn, their uncle, Madog killed Iorwerth in 1111.
He employed his uncle Maredudd ap Bleddyn as penteulu (captain of the guard).
Owain took vengeance for the killing of his father by gouging out Madog's eyes.