Florian Theobald discusses the understanding of the devil in the gospel of John and deals firstly with the representation of the devil in the early Judaic and Christian periods. In the first part ("The history of the representation of the devil from its beginnings to the New Testament") particular attention is paid to the theory of Henry Ansgar Kelly that in the writings of the early Judaic period and of the New Testament, the devil is to be understood not as an adversary but as a functionary of the Divine Government. The work also shows that the role of the devil in the early Judaic and New Testament texts is not clearly defined. He can appear in the same text as both an officer and an adversary of God.The second, main part of the work ("The devil in the Gospel of John") is concerned with the devil's nature and workings and his fall and loss of power in John's Gospel. The author shows how the devil in the fourth gospel is thought of as an objective figure outside of man but at the same time is clearly linked with psychological effects. Three dimensions of his psychological workings are apparent: 1. A cognitive dimension: the devil influences man's consciousness through the power of the lie so that people perceive and judge from worldly standpoints; 2. An ethical dimension: through his cognitive workings, the devil produces in man inappropriate behaviour. People carry out the will of the devil in the belief that they are doing God's will; 3. An emotional dimension: John's devil produces hatred and aggression, fear of death and - in accordance with a common tradition from the early Judaic period - sadness.Thus, the devil in the fourth gospel can be active in the world, even after his fall: after his loss of power on the cosmic level which occurred in the hour of Jesus there is also a need for his power to be destroyed on an anthropological level. This is achieved through the Paraclete and allows the disciples to participate in Jesus' victory over the devil.