There is an almost-humorous event that happened in the city of Ephesus, while Paul was ministering there (Acts 19:11-15). He had been so successful in proclaiming the name of the Lord Jesus, performing miracles in the name of the Lord and casting out demons in the name of the Lord that some imposters tried to duplicate his power over evil spirits by simply speaking the name “Jesus.” Their powerless attempt failed miserably, which led the demon to mock them.
Can you imagine this? The evil spirit spoke out, “Jesus I know” (i.e., a knowledge that is based on experience, recognizing Jesus’ authority). “Paul I know” (i.e., a knowledge that is acquainted with someone). “But who are you?” The demon had been troubled by Jesus and His deeds; the demon had been 
troubled by Paul and his deeds. But, these imposters had never done anything to show up on the demon’s radar of trouble, so he didn’t know them.
Makes me wonder: does the devil know who we are? Have we ever done anything to trouble him?