Demas is mentioned in the New Testament and appears to be a man who was a Christian, who was involved in the ministry of the gospel of Christ as a companion of the Apostle Paul, who later turned his back on the faith. He was with Paul during his first imprisonment in Rome, but later when Paul wrote Second Timothy he noted that "Demas had forsaken him, having loved this present world." See Colossians 4:14, 24 and 10.
Demas in fiction
The novel The Book of Demas by Leslie H. Whitten, Jr. tells a fictional account of the life of Demas.
The novel The Pilgrim's Progress by John Bunyan has a character Demas, a deceiver, who beckons to pilgrims at the Hill Lucre to come and join in the supposed silver mining going on in it.