Satan’s evil angels are known in Scripture as demons. The word for demons in the Greek language is daimon and is found more than 75 times in the Greek New Testament. In each case it is translated by the word devil in the King James Version.
We know from certain Scriptures that Satan fell from heaven and other angelic beings (demons) shared in Satan’s fall and became evil (Ezekiel 28:18; Matthew 25:41; Revelation 12:4).
The Bible provides abundant evidence of the existence of demons, see five below, among others.
Behemoth – (Job 40:15–24)
Beelzebub – (Matthew 10:25 ; Matthew 12:24 Matthew 12:27 ; Mark 3:22)
Belial – (2 Corinthians 6:15)
Chemosh – (1 Kings 11:7, 2 Kings 23:13)
Leviathan – (Job 3:8, Isaiah 27:1, Psalm 74:14, Psalm 104:25-26)