By virtue of stepping out of the chorus and creating dialogue is said to be both the first actor and playwright.

Thespis

Explanation:

According to some Ancient Greek sources, and Aristotle in particular,  Thespis was the first individual ever to appear on stage as an actor playing a  character in a play (instead of talking as himself).  

In other sources, besides the chorus, he is said to have introduced the first main actor.

It looks like that. Theorems and Proofs. It’s in geometry, a postulate is a statement that is assumed to be true based on basic geometric principles. But an example of a postulate is the statement like “ through any two points is exactly one line”.