Who is Anton Chekhov from The Art of Dramatic Writing and what is their importance?

The author mentions Anton Chekhov in reference to the strong perseverance of his characters in the chapter 'Strength of Will in a Character.' Chekhov's story, The Bear, is excerpted to exemplify great transitioning. The author compliments Checkhov's ability to write and says his plays will stand the test of time because his great characters are so adept at revealing themselves, as well as the era in which they are living.