The ‘burner’ who brought destruction upon Tara until he was slain by Fionn mac Cumhaill on the latter's first visit there. Aillén was a fairy musician of the Tuatha Dé Danann who resided at the sídh Finnachaid, also a home at different times to Lir. Every Samain [Halloween], Aillén would come to Tara playing on his timpán. After the men of Tara were lulled to sleep by his music, Aillén would spew forth flaming rock from his mouth and burn the dwelling to the ground. Each year Tara would be rebuilt, and for each of twenty-three years Aillén returned, until Fionn arrived on the scene. The hero first made himself immune to Aillén's musical charms by inhaling the poison of his own spear, whose point was so venomous as to forbid sleep. After this Fionn skewered Aillén with his poisoned point. T. F. O'Rahilly once argued that Aillén mac Midgna was really the Fenian hero Goll mac Morna, an assertion that has not found wide wide acceptance.