Aillen trechenn

Aillen Trechenn or Trechend is a monster in the folklore of Ireland. In Irish Gaelic Aillen Trechenn means triple headed - hence a monster having three heads. It was said to have inhabited a cave or ancient burial mound in County Roscommon. The creature was said to loath humans. It was supposed to have been destroyed by Amergin.

References

#Rose, Carol. (2000). Giants, Monsters and Dragons. Norton