Who dated Achtan inion Olc Acha?

Achtan, fl. c. 1st-2nd centuries AD, mother of Cormac mac Airt.

Art mac Cuinn ("son of Conn"), also known as Art Óenfer (literally "one man", used in the sense of "lone", "solitary", or "only son"), was, according to medieval Irish legend and historical tradition, a High King of Ireland.