Efnysien

Efnisien fab Euroswydd (also spelled Efnissien or Efnysien) is a sadistic anti-hero in Welsh mythology, appearing prominently in the tale of Branwen ferch Llŷr, the second branch of the Mabinogi.

Described by Will Parker as "a study in the psychopathic personality" and an "embodiment of the forces of anti-social disruption," he is the catalyst of the tale's ultimate tragedy, and is largely responsible for the destruction of both Ireland and the Island of the Mighty.

The Irish offer to make peace and build a house big enough to entertain Bendigeidfrân but hang a hundred bags inside, supposedly containing flour but actually containing armed warriors.

[8]Jeffrey Gantz describes him as, "[T]he controlling force of Branwen,...a story all by himself: progressively insecure and envious, cruel and sadistic, clever and resourceful, repentant and self-sacrificing.

Nikolai Tolstoy describes Efnisien as "the gallant if peevish Briton who selflessly sacrifices himself for his comrades", while he is characterised by Proinsias Mac Cana as a force of "irrational malice and hate".