Fear Doirich (literally Dark Man) is a villainous Druid featured in Irish mythology in events surrounding the hero Fionn mac Cumhaill and his wife Sadhbh.
History
According to the myth, Fear Doirich had sought Sadhbh to wife, but transformed her into a deer when she refused his advances. Fionn encountered her while hunting, and his hounds Bran and Sceólang recognized her as an enchanted human, having themselves been born of a woman who had been changed into a hound. Fionn's land proved to be the one place were Fear Doirich's spell could be undone and Sadhbh restored to human form; upon achieving this, she and Fionn were married, and she became pregnant. Unfortunately, Fear Doirich learned of this and transformed her back into a deer after Fionn left for a war; she was thus never seen again.