You know, in Islam, we believe that there is no fallen angles. Angels can never disobey God, they have no free will, their only mission is to serve God
Therefore we believe that Iblis, or as you refer to him in Christianity as Lucifer or Satan was not a fallen angel, we believe that he is a Jinn.
But don't get it wrong, not all Jinns are demons!
In Islam, Jinns will be judged at the day of judgement that means that they have free will. Allah created them from fire.
Therefore we find bad Jinns (Demons) and also good Jinns (Muslims, Christians, Jews...)
We even believe that humans, the ones who spread evil and make wars, can be demons too.
This is a beautiful recital of the sura (chapter) of Jinns