Professional actors (histriones) were organised in small companies (grex, caterva) under the direction of a sponsor (dominus). Most were slaves or freedmen from the eastern Mediterranean. An exception were mime performances, regarded as a lesser genre, in which citizens and even women (!) were permitted to form part of the companies.
The actors received money for their performances, but their pay differed greatly depending on their fame, and many lived in extreme poverty. Only a few theater performances took place in each city throughout the year, so actors had to augment their earnings with other artistic activities and tours to different cities. Although there were some outstanding exceptions, actors were generally regarded as vulgar and morally repugnant. Roman law discriminated against them and their profession was held to be ignominious.
To identify the characters in tragedies and comedies, actors wore masks or personae. Mime performances were spoken, and masks were not used. In pantomime, actors wore masks with closed mouths and remained silent, expressing themselves through gestures and body movements.
The beautiful mask above, is an exhibit of the Tarraco museum. It probably belonged to amateur performers or lixae, artists who followed soldiers and earned their money by improvisation. Also see my message 'Terra cotta mask at Noviomagus', August 2009. For other masks or theater images on various objects you can look: here!