Unas (Demons) was the host to a Goa'uld known to the population of the Medieval planet simply as the Demon. He was utilized by his master so he could scare the villagers of the planet by thinking he was a demon, so that they would offer sacrifices for him to leave.
In 1999, it took SG-1 and Mary, to be sacrifices, however SG-1 escaped its grasp and because Simon gave SG-1 their weapons. They were able to kill him, but not before his Goa'uld took the Canon, leader of the village, as a host. (SG1: "Demons")