Owain Ddanwyn (pronounced [ˈoʊain ˈðanwɨn] in Modern Welsh, Eugein Dantguin in Old Welsh) was a prince of North Wales, probably a King of Rhos in the late 5th century. The epithet Danwyn means "White-tooth" in Welsh.
Owain appears in various ancient Welsh genealogies as the son of Einion Yrth and the father of Cynlas Goch. One of these is given the title, 'Pedigree of (the Kings of) Rhos. According to the Bonedd y Saint, he was also the father of SS. Einion Frenin, king of Llyn, Seiriol, and Meirion. Other than these genealogies, no documentary evidence exists concerning his life.