Wilhelm Adler is one of those very whiney, annoying characters, whom you find yourself simultaneously feeling sorry for, and wishing to slap.
He's a recently-fired salesman, who could probably get his job back if he swallowed his pride. Now living in the same hotel as his retired, widowed, much more successful father, whom he's hoping to mooch money from.
Nearly every little thing sets him into a reminiscence about some poor decision, embarrassing incident, or plans gone awry in his past. He left college to pursue an acting career, based on a casual comment by a talent scout. Once in Hollywood, he gets nothing. He's ruined his marriage (I'll leave some details for you to discover), become estranged from his sister, and lost all his money in a crooked investing scheme.
And all he ever does is blame these things on other people, dream about how he could turn it all around "if only he could get a little money to start again anew" from his Dad, and grind his teeth in bitterness at those around him who don't properly appreciate his genius and potential.
It's all a bit much.
This story has the stink of failure as thick as "Death of a Salesman", the remorse over lost opportunities as deep as Joseph Heller's "Something Happened", the wallowing in past glory as pitiful as "The Sound and the Fury", and self-delusion as laughable as Jim Croce's song "Working at the Car Wash Blues". If you're into those things, you'll like this.
Personally, I liked Bellow's "Dangling Man" much better, but among critics, that seems to be a minority opinion. I wonder why.