The fairy musician who burned Tara each Samhain until defeated by Fionn was Aillen.
In the Irish tale The Boyhood Deeds of Fionn, Aillen—often spelled Áillen—is a fire-breathing Otherworld being known as “the burner.” Each year at Samhain, he came to Tara, the seat of the High Kings of Ireland, and attacked after putting the court to sleep with his music. Accounts describe him playing a harp or timpán before releasing his destructive fiery breath.
Fionn mac Cumhaill defeated Aillen by using a poisoned spear. He inhaled the poison to keep himself awake while the rest of Tara slept, then killed the attacker. This victory helped establish Fionn’s reputation and, in the traditional story, led to his becoming leader of the Fianna.
Samhain was a threshold festival associated with the opening of routes to the Otherworld, making it a fitting setting for Aillen’s annual assault. Aillen is easily confused with Fionn, who was the hero, or with other famous Irish warriors such as Oisín and Cú Chulainn; none of those figures was Tara’s musical fire-breather.