The Catechism in Questions & Answers

74. Is the Devil part of the invisible creation?

The Devil was originally one of the angels. As such he is part of the invisible creation. This angel rebelled against God and was cast out of heaven and the fellowship of God with his followers owing to his disobedience, envy, and lies.

Evil: see Questions 217. et seq.

“For [...] God did not spare the angels who sinned, but cast them down to hell.”
2 Peter 2: 4
“And the angels who did not keep their proper domain, but left their own abode, He has reserved in everlasting chains under darkness for the judgement of the great day.”
Jude 6