The Catechism in Questions & Answers

143. What is related about Jesus casting out evil spirits?

The gospels relate that Jesus cast out demons— which according to the understanding of the time were also the cause of various sicknesses—and so healed people. Jesus Christ was even recognised as Lord by the demons (cf. Mark 3: 11).

The New Testament describes ‘demons’ as evil spirits opposed to God, who according to the understanding of the ancient world, caused illness and sought to control human beings.