The Gou’ld are the villains of the Stargate SG1 universe. In the popular SyFy channel series, the story line goes that the ancient Egyptian gods and goddesses were in fact aliens from another galaxy who used technology to enslave the ancient Egyptians. As the story progresses, the ancient Aztec and Incan deities are trotted out as Go’uld, as well as the Sumarian, Babylonian and a few Hindu deities as well. So far the Celtic pantheons have been left untouched, and I imagine Yahweh and son Yeshua are simply too hot to paint with that brush (but I can’t wait until they do!).
Similar to Star Trek’s Trills: they share their bodies with ancient, snake like creatures with very long memories and vast knowledge who share a humanoid persons body in order to survive. The difference though is that the Gou’ld don’t share — they take over, much like the xtian faction of the Republican Party is attempting to do with this entire nation.