The concept of using masks in theater was born from worship of Dionyssos, the Greek god of fertility and wine.
There were a great amount of rituals and ceremonies that were associated with worship of Dionyssos and many of them included the wearing of masks.
The acting fraternity of Greece adopted the mask wearing proclivities of the worshippers of Dionyssos. In fact, Thespis, a Greek writer, was the first to wear a mask and it is from his name, Thespis, that we derive the word thespian, a synonym for actor.
One of the main reasons for the wearing of Greek masks in theater was the fact that there were female roles but women were forbidden from performing on stage. Therefore, men work female masks when they played the female roles.
The use of masks was also helpful when an actor had to play more than one role. A simple change of masks was all one needed to switch characters. There were some theories about the masks helping to accentuate the actor's voice but there are many that also discount this concept.
The masks were usually made of wood, cloth or leather and were as creative as the people who made them. Many of the masks were decorated with hair, either human or animal, to complete the effect. There was only a small hole drilled where the pupil of the eye would be for the actor to see through.
Every actor today owes a measure of gratitude to the ancient theater and the Greek masks that graced each and every stage. They were the forefathers of modern theater and by association, even television and the movies.