When summarizing the Gospel for the first Gentile converts, Peter described “how God anointed Jesus of Nazareth with the Holy Ghost and with power, who went about DOING GOOD and HEALING ALL who were OPPRESSED OF THE DEVIL; for God was with Him.” (Acts 10:38).
And we have many revelations in the New Testament about him, like these explanations of Jesus,
He was a murderer from the beginning, not holding to the truth, for there is no truth in him. When he lies, he speaks his native language, for he is a liar and the father of lies. John 8:44b.
The thief comes only to steal and kill and destroy; I have come that they may have life, and have it to the full. John 10:10.
Fallen angels are people like us, with a mind, will, and emotions. For example,
Acts 19:13-17 (NIV)
13 Some Jews who went around driving out evil spirits tried to invoke the name of the Lord Jesus over those who were demon-possessed. They would say, “In the name of the Jesus whom Paul preaches, I command you to come out.”
14 Seven sons of Sceva, a Jewish chief priest, were doing this.
15 One day the evil spirit answered them, “Jesus I know, and Paul I know about, but who are you?”
16 Then the man who had the evil spirit jumped on them and overpowered them all. He gave them such a beating that they ran out of the house naked and bleeding.
17 When this became known to the Jews and Greeks living in Ephesus, they were all seized with fear, and the name of the Lord Jesus was held in high honor.