This guy is basically the Christmas spirit personified: he's a jolly, polka-playing Midwesterner with a heart of gold. When he sees Kevin's mom in distress at the Scranton airport, he doesn't hesitate to try to help.
He swoops in and offers to give her a ride from Northeastern Pennsylvania (a place where certain people love polka—that's an accurate detail) back to Chicago. He and his band are headed to Milwaukee (a mecca of polka, we can assume) and Chicago's on the way.
Gus isn't just a helpful dude—he's funny too. He acts like being in a polka band is equivalent to being in a superstar rock group, where the stars neglect their children and wives. He says,
GUS: Gee, you want to talk about bad parents? Look at us. We're on the road forty-eight, forty-nine weeks a year. We hardly see our families. You know, Joe, over there. Gosh, you know, he forgets his kids' names half the time. Ziggy over there, he's never even met his kid. Eddy: let's just hope none of them write a book about him.
Trying to comfort Kevin's mom for leaving her kid home alone, he tells her:
GUS: I did leave one [of my kids] at a funeral parlor once. Yeah, it was terrible too. I was all distraught and everything. The wife and I, we left the little tyke there in the funeral parlor all day. All day. You know, we went back at night, when we came to our senses, there he was. Apparently he was there all day with a corpse. Now, he was okay. You know, after six, seven weeks, he came around and started talking again. But he's okay. They get over it. Kids are resilient like that.
This probably isn't the comforting message she was hoping for. But, if she's thinking that Kevin will end up traumatized, she can rest assured: tangling with the burglars hasn't scared him…it's only kindled his bloodlust.
So that's Gus—a helpful, jolly, kindly Christmas elf.