The name Ruadhan is a boy's name of Gaelic, Irish, Irish Gaelic origin meaning "red-haired". Ruadhan and is often added to lists like Redhead Baby Names and discussed in our forums with posts like "Picky Parents BNG".
From the experts:
Ruadhan is another spelling of the saints' name Ruadan, one of the Twelve Irish Apostles, but both have been anglicized and modernized (and simplified) as Rowan. Another Gaelic spelling is Ruadhain, but Rowan is preferable outside of Ireland.