Final answer:
Aeschylus significantly developed theatre by reducing the size of the chorus and introducing a second actor, enriching the dramatic experience. His most famous work is the Oresteia trilogy, consisting of 'Agamemnon', 'The Libation Bearers', and 'The Eumenides'.
Step-by-step explanation:
Aeschylus is widely regarded as a pioneer in the development of theatre, particularly through his contributions to the dramatic form of tragedy. He played a critical role in reducing the size of the chorus from fifty to twelve men and introducing the concept of a second actor, known as the deuteragonist. This significant innovation allowed for more complex interactions and dialogue-heavy performances, giving drama a new depth and dimension. Moreover, Aeschylus's emphasis on the dialogue over the choral part expanded the potential for storytelling in plays.
His most famous work is the Oresteia, a trilogy of plays comprising 'Agamemnon', 'The Libation Bearers', and 'The Eumenides'. It is notable not only for its comprehensive narrative, which explores themes of justice, vengeance, and divine intervention, but also because it is the only complete trilogy of Greek drama to survive to modern times.