Even his historical existence is not certain, some considering him only an avatar of the mythical Celtic king Gwar or Guéor, supposed to be buried under the tumulus of Roc'h Bleingor which overlooks the hamlet of Saint-Herbot [fr], Finistère.

[1][2] Christian tradition says that he belonged to a powerful family in Britain, that he came to Armorica and first settled in Berrien where he lived as a hermit in a forest, obeyed even by wild animals, working many miracles and converting many of the inhabitants.

[5] After he became the patron saint of horned beasts his cult spread widely, with 120 churches or chapels in Brittany housing a statue representing him.

[6] He was invoked among other things to make the cows give milk and to help with butter-making,[7] so that he is represented in St Collodan's Church in Plogoff with a lump of butter in his hand.

During epidemics his power is triumphant, and that is the time when on his altar stand, bloody and stinking, in the middle of swarms of flies, pyramids of cows' tails.