The se'irim, or sa'ir, were goat-demons that resided in the Ancient Levant, notably in the land of Bashan and around Mount Hermon, base of the watchers. The ancient Israelites were ordered by God to not worship or give offerings to the se'irim, alongside the shedim and Moloch, due to their demonic nature.
It was also likely that they were the servants of Azazel, one of the fallen watchers, a Prince of Hell and local desert deity. They might also have had a connection with Pan and the satyrs of Greece, since the horned would be later be worshipped in their domain by the Romans and Greeks.