Damarchus (Greek: Δάμαρχος) or Demaenetus was a victorious Olympic boxer from Parrhasia (Arcadia) who is said to have changed his shape into that of a wolf at the festival of Lycaea, only to become a man again after nine years.

The festival of Lycaea involved human sacrifice to Zeus. A young boy was killed and then consumed by one of the participants, in this case by Damarchus, and as a result Zeus would transform the cannibal into a wolf.

According to Pausanias’ Description of Greece, the werewolf could once again live as a man provided he abstained from human flesh for nine years; if, however, the wolf tasted the flesh of a man, he would remain a beast forever.

The Arcadians believed that the first king of Arcadia, King Lycaon, sacrificed his own son at a feast, which he then served to Zeus, his guest. In disgust, Zeus turned the king and his sons into wolves as punishment.

This gave rise to an annual sacrifice in which the clansmen of Arcadia would gather on the slopes of Mount Lykaion – or Wolf Mountain – for a similar ritual sacrifice to Lykaios Zeus. The flesh of a sacrificed young male would be mingled with the entrails of a wolf and presented to Lykaios Zeus; any young man who ate of the flesh would then be turned into a wolf for nine years.