Miles Bjornstam is known to many people in Gopher Prairie as the town "crank." Most people only see Miles when they absolutely need him, like when they need to get their houses ready for winter. In these cases, "The universal sign of winter was the town handyman—Miles Bjornstam, a tall, thick, red-mustached bachelor, opinionated atheist, general-store arguer, cynical Santa Claus" (7.1.2).
No one really likes Miles, because he pretty much believes the opposite of what the typical small-towners of Gopher Prairie believe. He's a socialist atheist who seems to get a real kick out of upsetting the dull conservatism of his small town.
To many people in Gopher Prairie, Miles is known as "Miles Bjornstam. Half Yank and half Swede. Usually known as 'that damn lazy big-mouthed calamity-howler that ain't satisfied with the way we run things" (10.3.30). Eventually, though, Miles gets married, has a kid, and settles down. He stops saying as many inflammatory things as he used to because he wants people to treat his wife and son well. In that respect, he, too, becomes a disappointment to Carol.
On top of that, once his wife and son die, Miles feels like he has nothing left to live for, so he moves out of town and robs Carol Kennicott of her only outlet for her rebellious political beliefs.