So, Satan is a Christian god, right?

Satan is not a god. He was an angel who tried to rise up and usurp god's authority and was therefore banished from the kingdom of Heaven. Angels are not gods. He sounds liek a god to you because you are a pagan and pagans have multiple gods and have nothing to do with Christianity. At least, not since the forced conversions. In Christianity there is only one god. Yhwh did not "wipe him out" because Satan was once the bright and shining star of Heaven; God's favorite. God banished Satan and gave him dominion (since that's what he wanted) over the earth and worms rather than the Kingdom of Heaven.