The captive control and influence of a person by an invisible wicked spirit. In Bible times demonized persons were afflicted in various ways: some were unable to speak, some were blind, some acted insane, and some possessed superhuman strength. All were woefully mistreated by these invisible bullies. (Mt 9:32; 12:22; 17:15; Mr 5:3-5; Lu 8:29; 9:42; 11:14; Ac 19:16) Men, women, and children were their victims. (Mt 15:22; Mr 5:2) Sometimes the agony was compounded when many demons gained possession of a person at the same time. (Lu 8:2, 30) When the demon was expelled, the person returned to a normal, sane state of mind. There is a difference between demon possession and  ordinary physical sickness and disease, for Jesus cured both types of disorder.​—Mt 8:16; 17:18; Mr 1:32, 34.

Some of Jesus’ greatest miracles involved the setting of possessed persons free from captivity to the demons. They were powerless against him. But not everyone was happy with his demon-expelling work. The Pharisees accused him of being in league with the ruler of the demons, Beelzebub, whereas in reality, as Jesus pointed out, they themselves were the offspring of the Devil. (Mt 9:34; 12:24; Mr 3:22; Lu 11:15; Joh 7:20; 8:44, 48-52) Jesus knew the source of the power that gave him mastery over the demons, and he openly confessed that it was Jehovah’s spirit. (Mt 12:28; Lu 8:39; 11:20) The demons themselves recognized Jesus’ identity and addressed him as the “Son of God,” “the Holy One of God,” and “Jesus, Son of the Most High God.” (Mt 8:29; Mr 1:24; 3:11; 5:7; Lu 4:34, 41; Ac 19:15; Jas 2:19) However, at no time would Jesus allow them to witness in his behalf. (Mr 3:12) On the other hand, a man who was set free from the power of the demons was encouraged to publish to his relatives ‘all the things Jehovah had done for him.’​—Mr 5:18-20.

Jesus also gave authority over the demons to his 12 apostles, and later to the 70 that he sent out, so that in the name of Jesus they too were able to cure the demon-possessed. (Mt 10:8; Mr 3:15; 6:13; Lu 9:1; 10:17) Even one not an immediate associate of Jesus or his apostles was able to exorcise a demon on the basis of Jesus’ name. (Mr 9:38-40; Lu 9:49, 50) After the death of Jesus, the apostles continued to have this power. Paul ordered “a demon of divination” out of a slave girl, much to the anger of her money-loving owners. (Ac 16:16-19) But when certain impostors, the seven sons of priest Sceva, attempted to cast out a demon in the name of “Jesus whom Paul preaches,” the demon-possessed man seized and severely mauled the seven of them and stripped them naked.​—Ac 19:13-16.

Often the wild and uncontrolled conduct of mentally unbalanced persons is due to possession by these invisible minions of Satan. Sometimes it is reported that spirit mediums have cast these demons out; this calls to mind what Jesus said: “Many will say to me in that day, ‘Lord, Lord, did we not . . . expel demons in your name . . . ?’ And yet then I will confess to them: I never knew you!” (Mt 7:22, 23) Compelling reasons, then, for heeding the counsel, “Be watchful,” and, “Put on the complete suit of armor from God that you may be able to stand firm against the machinations of the Devil” and his demons.​—1Pe 5:8; Eph 6:11.