Airgetmar, son of Sirlám, was, according to medieval Irish legend and historical tradition, a High King of Ireland.
The Lebor Gabála Érenn[1] says that, during the reign of Ailill Finn, he killed Fíachu Tolgrach in battle, but was forced into exile overseas by Ailill's son Eochu, Lugaid son of Eochu Fíadmuine, and the men of Munster.
He returned to Ireland after seven years, and, with the help of Dui Ladrach, killed Ailill.
Geoffrey Keating[2] tells a slightly different story of Airgetmar's accession.
The Lebor Gabála synchronises his reign with that of Artaxerxes III of Persia (358–338 BC).