Norm Gunderson is Marge's husband. Every time we see him with Marge—actually every time we see him in the film—he's either eating with her or watching TV in bed with her.
But this is a vision of domestic bliss: Marge and Norm root for each other and help each other out. Marge brings Norm a bag of worms for ice-fishing bait, and encourages him when his painting of mallard ducks only makes it onto the 3-cent stamp in a competition when another artist got the 29-cent. Norm supports Marge in her police work, as well, making sure she eats…and eats…and eats. He's quiet but very attentive to her.
NORM: I'll fix ya some eggs.
MARGE: That's okay, hon. I gotta run.
NORM: Gotta eat a breakfast, Marge. I'll fix ya some eggs.
MARGE: Aw, you can sleep, hon.
NORM: Ya gotta eat a breakfast. I'll fix ya some eggs.
MARGE: Aw, Norm.
The Coens had this to say about Norm:
Joel Coen: We were intrigued from the moment we started casting by the notion of very simple interplay between them and by the impassive expression of John Caroll Lynch, which seemed to suit the tone of the film perfectly.
Ethan Coen: He is the perfect incarnation of the undemonstrative personality of people from that region. The relations between husband and wife are based on what is not said, and yet they succeed nevertheless in communicating in some sense.
Norm seems to be employed as an amateur nature artist in the film, but is mostly a househusband. When the Coens started writing the film, they asked McDormand and Lynch to come up with a backstory for the characters. They decided that Norm used to be a cop as well, but when Marge got pregnant, they decided that only one of them should stay on the force. Since Marge was the better officer, Norm quit to stay home.
It's hard to get to know Norm because he doesn't say much, and is very undemonstrative. But from what we know about Marge, we trust that she's picked a solid guy. And you have to respect a man who can gaze into a bag of night crawlers and not let it interfere with lunch.