Which actor role is distinguished as "principles" in theater?

In theater, the term "principles" refers specifically to the lead roles or main characters within a production. These actors are typically at the forefront of the narrative, embodying the central themes and driving the story forward through their performances. They are often involved in the most significant scenes, have substantial dialogue, and are pivotal to the audience's understanding and engagement with the plot. Their roles require a higher level of performance skill since they carry the emotional weight of the story and are usually the focus of the audience's attention.

The other roles, such as supportive cast members or background characters, serve important functions but are not classified as "principles." Supporting cast members provide essential assistance and complement the lead roles, while background characters contribute to the setting and atmosphere but do not have a primary narrative focus. Production staff, which includes directors, stage managers, and other behind-the-scenes personnel, play crucial roles in the overall production process but are not considered actors in the traditional sense.