who can tell in the new testament who was Demas, and what was he doing as his responsibility?from the Epistle.

Answer 1

Demas is mentioned three times in scriptures.

In Colossians 4:14, Demas and Luke are with Paul when he writes his letter to the Colossians, and are mentioned as greeting them.

In Philemon 24, Demas is listed with Mark, Luke and Aristarchus as a "fellow laborer" who greets Philemon.

So it appears the Demas was a disciple who traveled for a time (probably in the last third of the book of Acts) with Paul and Luke. His specific responsibility are not given.

Finally, in his last letter (2 Timonthy 4:10), Paul writes and ask Timothy to hurry and join him, because everyone else has left Paul. He says that "Demas has forsaken me, having loved this present world, and is departed unto Thessalonica". It is often taken to mean that Demas turned away and deserted Paul at the end of Paul's life.

Beyond that, there is no other Bible information on the person of Demas.