Who were/are the most influential/important people in modern American literature?

Assuming that we’re using a standard definition of “modern” I’m putting the time period between 1914 and 1960(ish.) These are the years that are typically used when you define modern American literature. Anything between the wars, although the end date is variable.

I’m also assuming that you mean authors and not characters.

John Steinbeck wrote quite a bit during this time period and is a very prolific American writer. His novel Grapes of Wrath is considered one of the hallmarks of American literature.

TS Eliot is a wild card. Some people claim that is a British writer while most American scholars claim him too. His poem “The Wasteland” is brilliant. I find him fascinating. I’ve never met anyone who gets all of his textual literary allusions. The man was a genius, even if he had some strange political views.

Ray Bradbury is a very popular science-fiction author of the time. His novel Fahrenheit 451 is written just after the end of WWII and continues to have draw uncomfortable parallels with the viewpoints of today.

Bernard Malamud wrote The Natural, which features one of the first popular anti-heroes. Fascinating book. Completely different from the movie.

Harper Lee’s To Kill A Mockingbird is another classic. Written in 1962, she deals with characteristics of prejudice.

Jack Kerouac’s On the Road is one of the standards of the Beat poetry movement of the late 50’s. Beat poetry brought an entirely new perspective on performance art and the purposes of poetry, paving the way for a lot of current musical movements.

The Spoon River Anthology, by Sherwood Anderson compiled short stories written about everyday people, but taken from different perspectives. They are very intriguing.

Ernest Hemingway. So the man loved alcohol and bull-fighting, but he managed to produce some incredible works!

ee cummings showed us that punctuation and capitalizing are completely optional

Willa Cather wrote amazing pieces about the heartland of the United States.

I could really go on and on, but I hope this helps.