Irish novelist poet and short story writer author of ulysses a 1500 page novel that focused on single day in the lives three Dubliners?

The Irish novelist, poet, and short story writer you're thinking of is James Joyce.

His masterpiece, Ulysses, is indeed a sprawling 1500-page novel that follows the lives of three Dubliners, Leopold Bloom, Stephen Dedalus, and Molly Bloom, over the course of a single day, June 16, 1904.