Áillen (Aillen)

Surviving narrative sources do not supply a cosmogonic or genealogical origin for Áillen. He appears within the Fianna-cycle narratives, most notably in the episode preserved as part of the Boyhood Deeds of Fionn, where he is presented as a recurring supernatural menace to Cormac's court at Tara. The name Áillen (anglicized Aillen), glossed in modern summaries as 'the burner,' was also used as a personal name in ancient Ireland, indicating the epithet had onomastic currency beyond the single tale.

The supplied accounts do not provide a detailed physical description of Áillen's body, size, or features. Sources consistently characterize him by his actions and talents: he plays the harp or timpán, produces soporific music, and uses fiery breath to burn Tara. He is described as a non-human incendiary being—an entity associated with fire and destructive visitation—rather than through a fixed corporeal portrait.

Áillen's chief abilities in the extant narratives are musical enchantment and incendiarism. He plays the harp or timpán and lulls those present at Tara into a deep sleep with his music; while they are asleep he burns the royal site with fiery breath. His appearances are cyclical, occurring at Samhain (reported as November 1). In the preserved story, his recurrent burnings end when Fionn mac Cumhaill deliberately keeps himself awake (by inhaling the poison from his spear) and then slays Áillen—this narrative countermeasure is the recorded means by which his cycle was broken.