Satan/Luzifer is not the opposite of God but a opposing force to the creation and will of God. Luzifer is kind of the oldest teenager with a bad case of “I hate my creator” temper tantrum ever.

In that way Luzifer itself is already the antichrist, he is just missing a corporal manifestation on earth.

Well and Luzifer is, a lot like the named angels, Jesus and all the saints, a great loophole for monotheistic Christian religion around the first commandment.