Satan/Lucifer is not the opposite of God but a opposing force to the creation and will of God. Lucifer is kind of the oldest teenager with a bad case of “I hate my creator” temper tantrum ever.
In that way Lucifer itself is already the antichrist, he is just missing a corporal manifestation on earth.
Well and Lucifer is, a lot like the named angels, Jesus and all the saints, a great loophole for monotheistic Christian religion around the first commandment.
edit notes: Corrected german written Luzifer to Lucifer