Biróg

In the cycle of tales surrounding Balor, Ethniu (Eithne) is kept from men to prevent a prophecy that her son would kill Balor. In versions recorded in the 19th and later centuries, a figure named Biróg (Biroge of the Mountain) assists the man Mac Cinnfhaelaidh (identified with Cian in mythic retellings) to gain secret access to Ethniu in the tower on Tory Island. After Ethniu bears triplets and a Fomorian messenger drowns two of them, Biróg rescues the surviving infant from the harbour and returns him into the care network of his father, who gives the child in fosterage to Gavida the smith. In later literary retellings (e.g., Lady Gregory, T. W. Rolleston) this rescued child is associated with Lugh and Biróg is reframed as a druidess; other summaries describe her as a leanan sídhe or filidh, reflecting variant classifications across sources.

The available sources do not provide a detailed physical description of Biróg. Narrative and secondary summaries identify her variably by role — as a leanan sídhe or female familiar spirit, as a filidh (poet/seer), and in later literary retellings as a druidess — but these labels indicate differing social or functional presentations rather than an attested set of physical traits in the cited material.

Across the tale variants Biróg's demonstrated abilities are practical, clandestine, and protective rather than specified magical formulas: she enables clandestine access to the tower on Tory Island so that Mac Cinnfhaelaidh/Cian can reach Ethniu, she rescues the sole surviving infant after an attempted drowning, and she acts as a custodian/facilitator by returning the child to its father to be placed in fosterage. Different sources characterize her as a leanan sídhe (implying a familiar or spirit-associate), a filidh (implying poet-seer skills), or a druidess (in later retellings), but the core attested behaviors in the sources are aid in secret access, rescue of a child, and intermediary action on behalf of human principals.