Evil halves in folklore/mythology

Question

I'm researching the literature trope of a character's evil half manifesting (most notably Dr. Jekyll and Mr. Hyde) and I was wondering if there are any tales from mythology/folklore surrounding the concept. What I mean is a person's evil half manifesting as an independent being, not as much an evil twin/nemesis, but any help would be much appreciated.

Thanks in advance.

Answer 1

The main character in the ancient Irish Epic, Tain Bo Cuailnge (The Cattle Raid of Cooley), the teenage warrior hero, Cu Chulainn, is described in the Tain as experiencing a 'Battle Rage'. Normally Cu Chulainn was a paragon of virtue, exhibiting the characteristics that were valued by the warrior aristocracy of Iron Age (pagan) Celtic society: gentleness, generosity, loyalty, courage, etc... But, when overcome by his 'Battle Rage', Cu Chulainn became, not merely dangerous to his foes, but dangerous to anyone around him. He underwent a physical as well as emotional transformation, taking on the appearance of a monster.

Scholars of Medieval literature (the Tain, originally transmitted orally, was, with the introduction of Christianity, first committed to writing by Irish monks sometime in the early Middle Ages) have noted the parallel between Cu Chulainn's 'Battle Rage' and the figure in the Norse Sagas of the 'Berserker', a warrior who was also subject to a form of 'Battle Rage' that made him dangerous to anyone around them. So consumed by anger were they that Berserkers would resort to biting the edge of their shields (one of the pieces in the famous Lewis Chessmen, carved in 12th-13th century Scandinavia, is likely intended to depict a Berserker, shows a warrior biting the top of his shield). Note that, last I read, scholar's disagreed whether the Berserker was an actual historical phenomenon of the Viking Age (roughly 800 to 1000 C.E. / A.D.) or merely a literary invention of the 13th century, when the sagas were written.

It's common in many cultures to simultaneously and contradictorily revere and fear the warrior, who is at once both the defender of a community and a threat to peace within a community. If I'm not mistaken, I believe that in some native American and African societies, warriors returning from a battle were required to isolate themselves from their community and undergo some form of 'purification' ritual before they could re-enter the community.

Answer 2

Kudos to Paul for the Celtic / Scandinavian answer!

In Greek mythology, one of the best examples is Herakles (Hercules to you Romans), who was twice driven mad by the gods, and in his madness, killed his wife and children.

Also check out Euripides' Bacchae -- the whole mythology of Dionysian influence could very easily be compared to Jekyll and Hyde.

Getting a little more modern, you could look at werewolf mythology as well, though I don't know off the top of my head which sources I'd direct you to specifically.