Complex sentence: Ralph Ingersoll (c.1900--c.1984) was an American writer, editor, and publisher, probably best known as the founder and publisher of the short-lived 1940s New York City left-wing daily newspaper "PM".
Split into simpler sentences: Ralph Ingersoll (c.1900--c.1984) was an American writer, editor, and publisher. He was the founder and publisher of the short-lived 1940s New York City left-wing daily newspaper "PM".