Aillen or Áillen is a being in Irish mythology

Irish mythology

The mythology of pre-Christian Ireland did not entirely survive the conversion to Christianity, but much of it was preserved, shorn of its religious meanings, in medieval Irish literature, which represents the most extensive and best preserved of all the branch and the Historical Cycle. There are...

. Called "the burner", he is a member of the Tuatha Dé Danann

Tuatha Dé Danann

The Tuatha Dé Danann are a race of people in Irish mythology. In the invasions tradition which begins with the Lebor Gabála Érenn, they are the fifth group to settle Ireland, conquering the island from the Fir Bolg....

 who resides in Mag Mell

Mag Mell

In Irish mythology, Mag Mell was a mythical realm achievable through death and/or glory...

, the underworld

Underworld

The Underworld is a region which is thought to be under the surface of the earth in some religions and in mythologies. It could be a place where the souls of the recently departed go, and in some traditions it is identified with Hell or the realm of death...

. According to The Boyhood Deeds of Fionn

The Boyhood Deeds of Fionn

The Boyhood Deeds of Fionn is a medieval Irish narrative belonging to the Fenian Cycle of Irish mythology. As its title implies, it recounts the boyhood exploits of Fionn mac Cumhaill, the cycle's central figure...

, he would burn Tara

Hill of Tara

The Hill of Tara , located near the River Boyne, is an archaeological complex that runs between Navan and Dunshaughlin in County Meath, Leinster, Ireland...

 to the ground every year at Samhain

Samhain

Samhain is a Gaelic harvest festival held on October 31–November 1. It was linked to festivals held around the same time in other Celtic cultures, and was popularised as the "Celtic New Year" from the late 19th century, following Sir John Rhys and Sir James Frazer...

 with his fiery breath after lulling all the inhabitants to sleep with his music. This only ended with the arrival of Fionn mac Cumhaill

Fionn mac Cumhaill

Fionn mac Cumhaill , known in English as Finn McCool, was a mythical hunter-warrior of Irish mythology, occurring also in the mythologies of Scotland and the Isle of Man...

, who inhaled the poison from his spear to keep himself awake and slew Aillen. The act won him the leadership of the Fianna

Fianna

Fianna were small, semi-independent warrior bands in Irish mythology and Scottish mythology, most notably in the stories of the Fenian Cycle, where they are led by Fionn mac Cumhaill....

.

Aillen was also a popular personal name in ancient Ireland and was used by several personages. The fertility goddess Aine

Áine

Áine is an Irish goddess of love, summer, wealth and sovereignty. She is associated with the sun and midsummer, and is sometimes represented by a red mare. She is the daughter of Egobail, the sister of Aillen and/or Fennen, and is claimed as an ancestor by multiple Irish clans...

is also sometimes known by this name.