Deus Ex Machina is Greek for "God From The Machine." This item was used in Greek Theatre to give the impression of someone flying. This machine is still a delicacy in Film Making and Theatres today, but recently it has been replaced by CGI and Blue Screening.
The Deus Ex Machina was used rarely, but when it did appear, it did so in Comedy performances to display "something out of the normal".  Alternately it could be used in Tragedy, display angels warning people about hte unfortunate future or ghosts. They wouldn't use it to show someone dying, as violence was never shown in theatre. These were the most common uses of Greek Theatre, Comedy and Tragedy.
Both types of Greek Theatre used the according masks. {Tragedy on the left, Comedy on the right.} To make sure the focus was on the masks the majority of the time, only 2 actors (possibly less!) were ever on the stage at one time.
Tragedy is still one of the most popular themes today, and for that we thank "Aeschylus". He lived for 69 years and in that time, he wrote 3 large plays and one series of plays and most importantly, created Tragedy.  Tragic, really...